energy balance and thermogenesis in rats consuming nonstarch

ABSTRACTBackground: The equivalents of dietary protein, fat, and avail-able carbohydrate as fuels for maintenance (kJ apparent metabo-lizable energy/kJ maintenance requirement) are known fromclassical experiments and are similar across species; that fornonstarch polysaccharide (NSP) is undetermined.Objectives: Our objectives were to determine the energy equiv-alent of NSP and the thermic responses to NSP.Design: In a randomized block design, 120 rats were treated ingroups of 10 for 28 d with a basal diet (control) supplementedwith starch and 10 different NSP treatments in amounts between38 and 92 g/kg basal diet. Cellulose and starch were references.Thermic responses, deduced from body-composition changesand modeling of energy disposition, and energy and substrateexcretion were determined.Results: NSP had fermentabilities between 0.01 and 0.93 g/gintake. Fermentability, partial digestible energy, and net metabo-lizable energy values of NSP were closely related. Generally,51% of apparent metabolizable energy from NSP (fermentablegross energy) met maintenance requirements. Diet (energy)-induced thermogenesis (DIT) was evident from whole diets. Fer-mentable NSP supplied net metabolizable energy and causedDIT. After DIT and fermentation were accounted for, NSP-induced thermogenesis was generally 22 ± 4% (x– ± SEM) ofgross NSP energy, except for an outlying pectic preparation,which was 33% (P< 0.1).Conclusions: The energy equivalent of NSP was 196 (100/51)kJ/kJ, compared with 128, 105, and 100 for protein, fat, and glu-cose, respectively, from the classical experiments. With theexception of pectic NSP, NSP does not induce thermogenesis inexcess of that associated with DIT and fermentation.Am JClin Nutr 1998;68:802–19.

KEY WORDS Energy balance, thermogenesis, nonstarchpolysaccharide, fermentability, energy value, rats, humans

INTRODUCTION

Classical experiments have established how efficiently appar-ent metabolizable protein and fat meet energy requirements formaintenance compared with available carbohydrate in humans,dogs, and rats (1–4). The efficiency values, or equivalents,obtained experimentally are very close to theoretical ones on thebasis of estimates of high-energy bond yield in the metabolic

pathways (gain of ATP equivalents). On the basis of carbohy-drate (as glucose) having a value of 100 kJ by definition, othervalues are 105 kJ metabolizable fat and 128 kJ metabolizableprotein (5, 6). Studies on the energy equivalent of nonstarchpolysaccharide (NSP) have, so far, been scanty and those that areavailable appear to give a less simple view than is evident for themajor macronutrient energy sources.

Traditionally, NSP, or dietary fiber, has been viewed as a non-nutrient, with no physiologic energy value (7, 8). However, theavailability of energy from NSPs as short-chain fatty acids wasknown to early researchers and one—butyric acid—appears to beeither essential or conditionally essential for the health of thecolonic mucosa (9). NSPs are a diverse group of polysaccha-rides; some are fermentable and supply digestible or metaboliz-able energy and others are nearly nonfermentable and supply nosuch energy to metabolism (10–16). How efficiently the apparentmetabolizable energy from dietary NSP is used to meet energyrequirements is uncertain.

The soluble NSP guar gum is essentially completely fer-mentable without energy loss to urine; therefore, it yields anapparent metabolizable energy value of 17 kJ/g, the same as itsheat of combustion, but yields a partial digestible and metabo-lizable energy value of 10 kJ/g because of the associated rise infecal excretion of protein and fat. Furthermore, ingestion of guargum increases energy expenditure and makes no contribution tofat deposition, and so makes no net contribution to the mainte-nance energy requirement (17, 18); in other words, the netmetabolizable energy value of guar gum is practically 0 kJ/g.The metabolizable energy equivalent of guar gum for mainte-nance, compared with starch (or glucose), therefore, approachesinfinity because all the absorbable energy is balanced by addi-tional liberation of heat. A similar observation was made for themonosaccharide sugar D-tagatose, which is partly used by fer-mentation (19). Mechanisms underlying such thermic responses

Energy balance and thermogenesis in rats consuming nonstarchpolysaccharides of various fermentabilities1–3

Tracy Smith, Jacqueline C Brown, and Geoffrey Livesey

1From the Institute of Food Research, Norwich Laboratory, Colney, Nor-wich, United Kingdom.

2Supported by British Sugar Plc, Peterborough, United Kingdom, and theBiotechnology and Biological Sciences Research Council.

3Address reprint requests to G Livesey, Institute of Food Research, Nor-wich Laboratory, Colney, Norwich NR4 7UA, United Kingdom. E-mail:[email protected].

Received January 27, 1998.Accepted for publication May 6, 1998.

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to these 2 NSPs are not now known but increased costs of growthand maintenence of the alimentary tract have been suggested(19). Because the efficiency of systemic metabolism is remark-ably similar across species (20), and because some animals haveadapted to thrive on the energy from the end products of fer-mentation, notably ruminants, it seemed likely that our observa-tions with guar gum (and tagatose) would prove to be atypical ofNSP in general. Therefore, the present study to encompasses awide range of NSPs for the possible determination of a generalenergy equivalent.

We determined thermogenesis during the consumption byrats of 10 variously fermentable NSP preparations and askedwhether the amount of heat produced by the animals was eithersimilar to or more than theoretical amounts, as with guar gum(18). Thus, one-half of a carbohydrate’s gross energy, when fer-mented, is predicted on theoretical grounds to be available forthe purposes of maintaining energy balance (10, 21–25). In thepresent study, thermogenesis (heat production) was estimatedindirectly from changes in body composition and the efficiencyof fuel utilization for protein and fat deposition (18, 26, 27). Wegive a full description of the basis of various calculations madewith reference to a new schematic model of energy balancedeveloped for the present purpose, but which is in principleapplicable to any combustible substrate or thermogenic drug.The schematic calculations are accompanied by examples tofacilitate understanding of their execution. Also, we show how,by using minimization techniques, diet (energy)-induced ther-mogenesis (DIT) due to eating energy from NSPs can be distin-guished from a sum of NSP-induced energy expenditure andother associated energy losses that are difficult to measure.Finally, NSP in dietary fiber preparations may be accompaniedby lesser amounts of other organic (combustible) and inorganic(noncombustible) substances such as lignin, protein, fat, andash. This study used suitable procedures for assessing error andthe limits of such error that may have arisen in the outcomesbecause of accompanying substances.

MATERIALS AND METHODS

Materials

Starch was native cornstarch (Corn Products, Manchester,United Kingdom). Cellulose was Solka-flock (grade B92030;Johnson, Jurgensen and Wettre Ltd, London). Sugar beet fiber(SBF) was Betafibre (British Sugar Plc, Peterborough, UnitedKingdom). Other materials were prepared from sugar beet byBritish Sugar Plc: hemicellulosic and cellulosic NSP (soluble andinsoluble in water at 1008C, respectively), pectic NSP (solubi-lized in nitric acid at pH 1.5 for 1 h at 808C), and 2 others welabeled fiber L and fiber K (prototype commercial products; UKPatent Application no. PCT/GB90/00466). Fiber L and fiber Kwere extracted by a procedure similar to that for the hemicellu-losic NSP. Several related terms are used for these materials. Weuse the term “dietary fiber preparation” as a general descriptionof material containing much NSP, but it may also include closelyassociated substances, such as lignin and variable amounts ofresistant starch. The term “unavailable carbohydrate” is usedspecifically to mean carbohydrate that is not absorbed as carbo-hydrate in vivo; in general, it includes both NSP and resistantstarch but not associated substances such as lignin. For prepara-tions used in this study, there was no resistant starch and minimal

amounts of lignin (<2% in the SBF and cellulosic NSP prepara-tions), so dietary fiber, NSP, and unavailable carbohydrate areessentially synonymous. Dietary fiber preparations, on the otherhand, may include more than unavailable carbohydrate and thesubstances closely associated with NSP. The NSP, lignin, mois-ture, ash, nitrogen (as crude protein), starch, lipid, andethanol:water (80:20, by vol)-soluble oligosaccharide content ofthe preparations is given in Table 1. All NSP preparations exceptthe cellulosic one and SBF were nearly white powders, suggest-ing the absence of Milliard (browning) products, which are oth-erwise probably included in the lignin analysis.

Animals

Routine animal care and experimental procedures were inaccordance with the statutory regulations and ethical guidelinesof the United Kingdom Home Office. One hundred thirty spe-cific pathogen–free, male Wistar rats weighing <100 g (A Tuckand Son, Battlebridge, Essex, United Kingdom) were housedindividually in polypropylene cages with wire-mesh floors androofs (type RB3; North Kent Plastics Ltd, Dentford, UnitedKingdom). The room was maintained at 21± 18C, lit from 0600to 1800, and drinking water was made freely available.

Protocol

Rats consumed a diet for 14 d that had 50 g SBF added to each100 kg basal diet (diet F, Table 1) to adapt them to the source ofthe various fermentable NSP treatments before the energy bal-ance measurements. Consumption was ad libitum for the first 4 d(mean: 19 g per animal daily) and 80% of ad libitum thereafter(15.2 g per animal daily). Using computer-generated randomnumbers, we allocated animals to 13 groups of 10 rats each. Onegroup was killed for analysis of body composition and theremaining groups each consumed one of the diets listed in Table1 for 28 d: a basal diet, a starch-supplemented diet, diets supple-mented with 3 different amounts of SBF, and comparable singledoses of other NSP preparations (Table 1). Food was provided at<0900 each day and all rats received similar amounts of basaldiet (15.2 g per rat daily), which met protein (casein), vitamin,and mineral requirements (28); the supplementary NSP was addi-tional. At the end of the 28-d period, all remaining animals werekilled for body-composition analysis (18). The food provision,spillage, intake, and fecal collections during the final 14 d of thedietary treatments were determined as usual (18). Food spillagewas usually negligible because feed rations were less than ad libi-tum intakes; when spillage occurred, the amount of food spilledwas added to the next ration of food to ensure that all animalsconsumed the required amounts of food throughout the balanceperiod. Because a large number of rats were used, each group wasdivided into 2 rooms and the dietary treatments were started with2 animals per group, 1 from each room on each of 5 consecutivedays. Animals were killed in the morning by cervical dislocationafter intraperitoneal injection of sodium pentobarbital anesthetic(60 g/L; 1 mL/g body wt) and emptied of digesta.

Analyses

The NSP and 80% aqueous ethanol–soluble oligosaccharidecontents of the dietary fiber preparations were determined by themethod of Englyst and Cummings (29); both acidic and neutralpolysaccharides were measured and lignin was determined asKlason lignin. Heats of combustion, Kjeldahl nitrogen, fat, andash determinations were as described by Brown and Livesey

ENERGY BALANCE AND NONSTARCH POLYSACCHARIDES 803

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(18). The lean mass of animals was the difference between drymatter and the fat content of the empty carcass. Carbohydrateenergy in feces was gross fecal energy minus energy as bothfecal fat and fecal protein (seecalculations below).

Data resource and error bounds

A data resource (Table 2) was required to facilitate certaincalculations. Errors in the resource data potentially propagateerrors in the energy and fermentability values calculated fromthe present experimental measurements. Upper and lowerbounds to such propagated errors were therefore estimated byrepeating the calculations by using the upper and lower errorbounds or combinations thereof for the resource data, which aregiven in Table 2. Thus, extreme estimates of the resulting errorbounds were obtained by assuming that errors propagated addi-tively and productively by using error bounds in the same direc-tion for additions, subtractions, and multiplications and of theopposite direction for divisions; ie, no one potential error wasbalanced against another.

Calculations

The components of energy balance through which energy is lib-erated during digestion and metabolism are shown schematicallyin Figure 1. Digestible energy is the difference between grossenergy intake and fecal energy excretion (Figure 1). Thus, thedigestible energy value of a supplement (DEVs; kJ/g) was calcu-lated in equation 1 from gross energy or heat of combustion (DHc;kJ/g) of the supplement minus the increment in energy excretionin feces due to eating the supplement (kJ/g supplement intake).The latter was obtained by a procedure that minimized the sensi-tivity to measurement errors (37) and is given by the term in

square brackets in equation 1, where E is gross energy (kJ) and Mis mass (g) of the basal portion of the diet or supplement, with sub-scripts t, c, d, s, and f for test, control, diet, supplement, and feces,respectively. The calculation gives what has been called the partialdigestible energy value (11, 37).

DEVs = DHc2 3(Etf/Mtd) 2 (Ecf/Mcd)4 (1)Ms/Mtd

Note that partial digestible energy values may potentially falloutside the range of 0 to DHc (11) and may reflect interactionsbetween basal dietary components and the NSP (18).

For each supplement, calculations were made of its net metab-olizable energy value (NEVs), which is the energy made avail-able per unit mass of supplement for the support of maintenanceenergy expenditure (including behavioral activity), energy stor-age, and DIT (including changes in behavioral activity associ-ated with change in energy intake). The calculation procedure iscomplex (Eqs 2–18) so the schematic description of the relevantcomponents of energy balance in Figure 1 was constructed tofacilitate understanding.

NEVs (Eq 2) is less than DEVs (Eq 1) because of nonfecalsupplement–induced energy losses (SIELnf), which comprise 1)gaseous and fermentative energy (hydrogen, methane, othervolatile combustibles, and heat of fermentation); 2) urinaryenergy; 3) heat losses due to the relatively inefficient high-energy bond yield (ATP gain) from, eg, short-chain fatty acidproducts of fermentation; and 4) supplement-induced energyexpenditure (Figure 1). The last item includes all other potentialsources of energy expenditure associated with ingestion of thesupplement other than DIT. In the current study, none of these 4

804 SMITH ET AL

TABLE 1Compositions of the basal, starch- and nonstarch polysaccharide (NSP)–supplemented diets1

Supplement Supplement composition2Total

Diet Supplement amount Moisture NSP Lignin Lipid Crude protein Ash Total NSP

g/kg basal diet g/kg fresh wt g/kg basal diet

A —B Starch 100 134 (866)3 — 1 3 — 1004 (87)3

C Cellulose 100 80 920 — 5 0 — 1005 92D SBF 150 90 750 17 13 80 55 1005 113E SBF 100 90 750 17 13 80 55 1005 75F SBF 50 90 750 17 13 80 55 1005 38G Hemicellulose 92 100 900 — 2 34 38 1074 83H Pectic 110 139 750 — 9 33 114 1045 83I Cellulose 132 119 630 20 18 112 54 952 83J Whole beet 1094 136 832 18 17 04 42 1045 83K Fiber K 100 129 830 — 4 17 53 1033 83L Fiber L 100 80 830 — 5 23 93 1030 83

1Basal diet: (g/kg) maize starch (10% moisture, Snowflake; Corn Products Ltd, Manchester, United Kingdom), 326; sucrose (Silver spoon; British SugarPlc, Peterborough, United Kingdom), 326; casein (edible, mesh 30; G Fiske and Co Ltd, Richmond, United Kingdom), 168; maize oil (Mazola; J Sains-bury’s, Norwich, United Kingdom), 80; cellulose (Solka-floc, grade BW2030; Jurgenson & Wettre Ltd, Woking, United Kingdom), 40; mineral mix, 40; vit-amin mix in starch, 20. The mineral mix produced (g/kg basal diet): CaHPO4, 13; CaCO3, 8.2; KCl, 7.04; Na2HPO4, 7.4; MnSO4·H2O, 0.18; MgSO4·4H2O,4; ZnCO3, 0.1; FeSO4·7H2O, 0.144; CuSO4, 0.023, KIO3, 0.001. The vitamin mix provided the following (mg/kg basal diet): nicotinic acid, 60; cyanocobal-amin in mannitol, 50; calcium D-pantothenate, 40; thiamine hydrochloride, 10; riboflavin, 10; a-pteroyl-monoglutamic acid, 10; pyridoxine, 10; biotin, 1;menadione, 2; Rivomix E-50 (containing 7.5 mg RRR-tocopheryl acetate, Roche, Welwyngarden City, United Kingdom), 150; Rivomix A-500 (containing3.75 mg retinol, Roche), 25; Rivomix D3-500 (containing 0.19 mg cholecalciferol, Roche), 15; choline bitartrate, 1800; maize starch carrier, 17.8 g. SBF,sugar beet fiber.

2There was <10 g/kg starch and oligosaccharides in 80% aqueous ethanol in the preparations.3Values in parenthesis show starch, not NSP.4A diet mixture (671.5 g) was made as above for the basal diet but with less sucrose and starch to compensate for the metabolizable energy in sucrose

(310 g) and protein (18.5 g) in the whole-beet preparation.

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components of energy balance was measured individually andnos. 3 and 4 were not measurable independently, but the sum(SIELnf) is an estimable quantity described further below. Thus,the net metabolizable energy value of an ingested supplement (Is,g) was as follows:

NEVs = DEVs2 (SIELnf /Is) (2)

In principle, SIELnf can be calculated from digestible energyintakes and body-composition changes by using a basic approachdescribed previously (18, 19, 26, 27). We modified this approachto allow a separate estimate to be obtained of DIT, which can thenbe excluded as a possible cause of NSP-induced thermogenesis.In the current approach, digestible energy intake is calculated asthe sum (Eq 3) of energy from the basal portion of the diet, forwhich Mb is its mass and DEVb its digestible energy value, andfrom the supplement for which Is is its mass and DEVs itsdigestible energy value. From Figure 1 it follows that digestibleenergy intake (DE; kJ) is also the sum (Eq 4) of SIELnf, DIT,energy used in the storage of fat (1.36EF) and protein (2.25EP)and energy required for maintenance (MEm). The values 1.36 and2.25 in equations 4–6 are the energies (kJ) required to deposit 1kJ energy as fat and protein, respectively (Table 2). Variability inthese energy costs is small and similar across species, as notedpreviously (18, 20, 30), and potential errors due to variation inthese costs are accounted for by using error bounds (seeTable 2).EF and EP were calculated as 39.3 kJ/g fat deposited and 20 kJ/gdry lean matter deposited, respectively, as determined previously(17) and potential error in these values was accounted for witherror bounds (Table 2). Rearrangement of equation 4 gave equa-tion 5, from which it is clear that the sum of MEm, SIELnf, andDIT is equated to the measured or known quantities (KQ) ofdigestible energy intake and change over time in body composi-tion (1.36EF and 2.25EP) (Eq 6).

DE = Mb 3 DEVb + Is 3 DEVs (3)

DE = SIELnf + DIT + 1.36EF + 2.25EP + MEm (4)

MEm + SIELnf + DIT = DE 2 1.36EF 2 2.25EP (5)

KQ = DE 2 1.36EF 2 2.25EP (6)

The difference (Eq 7) between the sum of MEm + SIELnf +DIT for animals consuming a test diet (td) and the sum for ani-mals on the basal control diet (cd), for which SIELnf and DIT arezero by definition, gave the value of SIELnf + DIT of the test arti-cle (t), because MEm cancels out. Substituting from equations 5then 6 gives equation 8, which has less variance after being nor-malized to the average lean (AL, g) dry mass of animals duringthe treatment period (Eq 9). The reason for lower variability isthat KQ varies largely because of variance in MEm (Eqs 5 and 6).AL was the average of the dry lean body mass (DLBM) obtainedat the beginning (zero) and end (28 d) of the balance period (Eq10). Carcass analysis gave DLBM at the end of the balanceperiod; at the beginning it was derived as a product of the treat-ment animal’s live weight on day 0 and the ratio of the DLBM tolive weight obtained for animals killed on day 0. (This is a pro-cedure suitable only for relatively lean animals, such as the diet-restricted juvenile rats in the present study.) The calculation ofAL (Eq 10) implies linear growth and was chosen as the simplestdenominator for reasons discussed previously (18).

(SIELnf + DIT)t =(MEm + SIELnf + DIT)td 2 (MEm + 0 + 0)cd (7)

(SIELnf + DIT)t = KQtd 2 KQcd (8)


TABLE 2Resource data: a priori parameter estimates and their error bounds1

A priori parameter estimate Value Error bounds

Miscellaneous valuesCost of body fat depostion (kJ/kJ) 1.36 1.08, 1.682

Cost of body protein depostion (kJ/kJ) 2.25 1.38, 3.272

NSP energy in feces (kJ/g fecal NSP) 17.5 16.6, 17.53

Nitrogen-associated energy in feces dueto extra NSP ingestion (kJ/g fecal N) 148 118, 1634

Heat of combustion (kJ/g)Body fat 39.3 37.3, 41.25

Body lean matter 20 19, 205

Basal dietary protein 23.6 22.4, 24.86

Basal dietary fat 39.3 37.3, 41.36

Protein in dietary fiber preparations 23.6 21.4, 25.67

Fat in dietary fiber preparations 39.3 37.3, 41.48

Lignin in dietary fiber preparations 35 31.5, 38.59

Digestible energy value (kJ/g)Protein in dietary fiber preparations 21.2 11, 2610

Fat in dietary fiber preparations 37.3 34.5, 41.411

Lignin in dietary fiber preparations 8.8 0, 1912

Net metabolizable energy value (kJ/g)Protein in dietary fiber preparations 14 6, 1913

Fat in dietary fiber preparations 35.5 32, 3914

Lignin in dietary fiber preparations 2.2 0, 815

1NSP, nonstarch polysaccharides.2A priori parameter estimates determined in Wistar rats (30), the error

bounds are± 2 SDs.3A priori assumption that fecal NSP has the highest heat of combustion

from the range of possible values; this due to NSP with low values beingthat which is readily fermentable (31). Error bounds are the same as therange of values for NSP in foods (31).

4A priori assumption that the additional fecal nitrogen associated withadditional NSP ingestion is mainly microbial protein (32). The errorbounds are set at ± 20% of the assumed value.

5As determined previously (17), with error bounds at ±10%.6Heats of combustion of casein and corn oil with error bounds at 2 SDs

for combustion calorimetry (15).7General heat of combustion for protein (33) with error bounds set at

±10%.8General heat of combustion for fat (33) with error bounds set at ±5%.9The heat of combustion is assumed to be the same as its principle poly-

mer polyphenyl-propane (34) with error bounds set at ±10%.10Estimates based on the heats of combustion shown and the general

digestibility value of 0.9 (33) with wide error bounds, 0.5 and 1.0.11Estimates based on the heats of combustion shown and the general

digestibility value of 0.95 (33) with wide error bounds, 0.8 and 1.0.12Estimates based on the heats of combustion shown and the general

digestibility value of 0.25 (35) with wide error bounds, 0.0 and 0.5.13Estimates based on the digestible energy value shown and an esti-

mated efficiency for use as net metabolizable energy of 0.6 (5,12), witherror bounds of 0.5 and 0.7.

14Estimates based on the digestible energy value shown and the esti-mated efficiencies for use as net metabolizable energy of 0.95 with errorbounds of 0.7 and 0.98 (33).

15Estimates based on the digestible energy value shown and the esti-mated efficiency for use as net metabolizable energy of 0.25 with wideerror bounds: 0.0 and 0.6 (35, 36).

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[(SIELnf + DIT)/AL] t = (KQ/AL) td 2 (KQ/AL) cd (9)

AL = (DLBM day 0 + DLBMday 28)/2 (10)

Differences in DIT between treatments were adjusted to zerovia covariance of KQ/AL with net metabolizable energy intake(NME), as described further below. Thus, DIT in equations 8 and9 became zero, simplifying equation 9 to a usable equation 11.The calculation of NME and the computation of covariancebetween KQ/AL and NME/AL are described in the next section.

(SIELnf/AL) t = [ (KQ/AL) td 2 (KQ/AL) cd ] DIT = 0 (11)

Finally, the left side of equation 11 was divided by the weightof supplement ingested (Is/AL; g/g) to obtain SIELnf per unitweight of supplement intake (Eq 12) and the net energy value ofthe supplement was calculated according to equation 13 (an iter-ation of Eq 2).

SIELnf /Is = (SIELnf/AL) t/(Is/AL) (12)

NEVs = DEVs 2 SIELnf/Is (13)

Calculation of NME and computation of DIT

The above derivation of NEVs required the computation ofDIT, and this computation required estimates of NME intake foreach diet to be calculated. To calculate NME we adopted theprinciple that accuracy is maximized when beginning with aknown energy intake and deducting estimated energy losses (12,37). Thus, we began (Eq 14) with the digestible energy intake ofthe diet and deducted the expected losses to urine and to heat.The expected losses are given by differences in digestible andnet metabolizable energy values for both the basal portion of thediet and the supplementary components (Table 2). In equation14, DEVb and DEVs are the digestible energy values (kJ/g) of thebasal diet (b) and supplement (s) with intakes of mass Mb and Is,respectively. Ppr, Pfat, Plg, and PNSP are the mass proportions ofprotein, fat , lignin, and NSP, respectively, in the basal diet andsupplement. The values 7.2, 1.8, 6.6, and (1 2 f)DEVNSP inequation 14 are the respective differences between digestible andnet metabolizable energy values (kJ/g; Table 2) and f is the frac-tional efficiency of converting DEVNSP to NEVNSP, which is anunknown to be solved. In equation 14, the term Mb(7.2Ppr +1.8Pfat)b differed between treatments only because of minor vari-

806 SMITH ET AL

FIGURE 1. Components of energy balance. Gross energy intake separates into fecal energy and “digestible energy,” which separates into gaseousand fermentative energy (i) and “absorbable energy”, which separates into urinary energy (ii) and metabolizable energy, which separates into energylosses associated with inefficient high-energy bond yield from a substrate compared with glucose (iii) and net metabolizable energy, and so on. Thesum of components (i + ii + iii + iv) gives the nonfecal substrate (or supplement)-induced energy losses (SIELnf). This sum can be deduced from othercomponents (seeEqs 2–18). [Addition of FE to SIELnf yields the total substrate or supplement-induced energy loss as defined previously (18).] Theenergy expended on fat (0.36 3 EF) and protein (1.25 3 EP) and energy deposited as fat (1 3 EF) and protein (1 3 EP) when added together give theenergy used in energy storage (1.36EF and 2.25EP). Digestible energy is in quotation marks because some authorities exclude gaseous energy fromfecal energy when defining digestible energy. Thus, digestible energy in human nutrition has traditionally not excluded gaseous energy on the groundsthat it is usually very small. Absorbable energy is also given in quotation marks for the same reason, but also because gaseous energy (hydrogen andmethane) is partly excreted via breath. In principal, the components of energy balance apply to any animal for any diet or dietary constituent; eachcomponent is variable in size relative to another so the relative bar lengths and areas are not given as typical.

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ations in the intake of basal diet (Mb) between treatments. Thecontribution to NME of the sum of products (7.2Ppr + 1.8Pfat 26.6Plg)s was also small because it accounted for contamination ofthe NSP preparations with protein, fat, and lignin. The product (12 f)DEVNSP 3 PNSP had the largest effect on variation in NMEbetween treatments and so it had the largest effect on the parti-tion of energy losses between DIT and SIELnf/Is when equation15 was used to zero DIT among treatments. PNSP was known,DEVNSP was estimated for each NSP supplement (and starch)from the composition of the supplement and its digestible energyvalue (Eq 1) as described below for equation 16, and f wasfound by minimization as described for equations 17–20.

NMEdiet = Mb 3 DEVb + Is 3 DEVs

2 Mb(7.2Ppr + 1.8Pfat)b 2 Is[7.2Ppr +1.8Pfat + 6.6Plg + (1 2 f)DEVNSP 3 PNSP]s (14)

To equalize DIT among animals, we used regression analysiswith NME/AL included as a covariate (Eq 15) for KQ/AL.Dummy variables (ie, 0 or 1) allowed the adjusted values ofKQ/AL [ie, (KQ/AL) DIT = 0] to be obtained as constants c1 to cn

(n treatments). ßDIT was the increase of energy expenditure [(DIT+ MEm)/AL] with increase in NME/AL and e was the residualerror (RSD). We adjusted values of NME/AL for each animaltoward the experimental mean value, (NME/AL)exp mean.

KQ/AL = c1 + c2... + cn +ßDIT [(NME/AL) animal 2 (NME/AL) exp mean] ± e (15)

Estimation of the energy values of NSP from the energyvalues of the supplements

The NSP preparations included contaminating ash, protein,lipid, and lignin (Table 1). We therefore present energy valuesfor both the supplements as a whole and for their NSP contents.The latter was calculated by using the principle that the whole isthe sum of the component products. Thus, any energy value (eg,DHc, DEV, and NEV) of the NSP (ENSP; kJ/g NSP) is equated inequation 16 with the corresponding energy value of the wholesupplement (Es; kJ/g Is), the corresponding energy values for thecomponents (Epr, Efat, and Elg; kJ/g) and the proportions (g/g Is)of the supplement accounted for by the components, protein(Ppr), fat (Pfat), lignin (Plg), and NSP (PNSP). For this purpose, weused the values of DHc, DEV, and NEV, and their error bounds,for these components given in Table 2.

ENSP (kJ NSP/g NSP) =[(Es 2 (Epr 3 Ppr) 2 (Efat 3 Pfat) 2 (Elg 3 Plg )]/PNSP (16)

Solving for f, the efficiency of using DEVNSP for NEV NSP

The calculations developed so far require a value for f inequation 14 before the eventual calculation of NEVs (Eqs 2 and13) and therefore NEVNSP (Eq 16,when E = NEV). A solution isfound by setting up 2 equations (Eqs 17 and 18) in f to yieldNEVNSP and finding the value of f between 0 and 1 that mini-mizes the differences in yield between the calculations. In equa-tion 17, NEVNSP is by definition the product of DEVNSP and f,the efficiency of using DEVNSP for NEVNSP. Equation (18) alsoarises by definition, being identical in form to equation 2, butnow applied to NSP rather than to the supplement as a whole.(That is, NEVs, DEVs, and SIELnf in Eq 2 are substituted byNEVNSP, DEVNSP, and NSPIELnf, respectively, in Eq 18, where

NSPIELnf is the nonfecal NSP-induced energy loss.) In practice,the yield for equation 18 was obtained by repeating the calcula-tions of equations 2–16 for values of f between 0 and 1.

(NEVNSP)f = 0 to 1= f(= 0 to 1) 3 DEVNSP (17)

(NEVNSP)f = 0 to 1 = DEVNSP 2 (NSPIELnf/INSP)f = 0 to 1 (18)

The solution for f was the value that resulted in the lowestsum, for NSP treatments 1 to n, of absolute differences betweenthe results of equations 17 and 18.

Calculation of fermentability and other theoreticalestimates of energy values

The fermentability of the supplementary unavailable carbohy-drate (UCs; g) was calculated as its apparent digestibility (D) byusing equation 19, which is structurally similar to equation 1, forthe calculation of digestible energy value. The unavailable car-bohydrate in the control (c) and test (t) diets (d) was that meas-ured in the supplement by using Englyst and Cummings methodfor NSP plus the cellulose in the basal diet. For the present pur-pose, unavailable carbohydrate in feces (f) was carbohydratedetermined by the difference between fecal gross energy (Ef) andenergies in fecal crude protein and fat (Eq 20; 5). Conversionfrom unavailable carbohydrate in energy terms to mass used 17.5kJ fecal UC/g (Eq 20). Fecal crude protein energy was estimatedfrom fecal nitrogen (148 3 fecal nitrogen,Nf), and fat energyfrom fecal fat (39.3 3 fecal fat,Ff). Uncertainty about the factorto convert fecal nitrogen to protein energy may lead to someerror in estimates of fecal protein but less error in the apparentdigestibility because the latter is a difference estimate. Never-theless, the reliability of the procedure was assessed by compar-ing the results it gave with known values for cellulose and thecurrent SBF preparation, which were established in interlabora-tory comparison trials (15) from analysis of NSP in food andfeces (seeDiscussion).

D = 12 3(UCtf/Mcd) 2 (UCcf / Mtd)4 (19)UCs/Mtd

UCf = (Ef 2 148Nf 2 Ff)/17.5 (20)

For certain arguments, it was useful to express the fer-mentability of NSP in units of energy (d; kJ/kJ), in which case,equation 19 was modified by multiplication of unavailable car-bohydrate by its heat of combustion. For unavailable carbohy-drate in feces this was 17.5 kJ/g; for supplemental unavailablecarbohydrate fermentability was calculated (Eq 16) from the adi-abatic bomb calorimetry determination of DHc for the supple-ment and the prior estimates for the heats of combustion of thecontaminants in the supplement (Table 2).

d = 12 3(17.5 3 UCtf /Mcd) 2 (17.5 3 UCcf/Mtd)4 (21)DHc 3 UCs/Mtd

Note that the values of D and d calculated by equations 19 and21, respectively, may result in values outside the range of 0 to 1in the same way that values of DEVs may fall outside the rangeof 0 to DHc.

Three other energy values related to the fermentability ordigestibility (D) of the supplementary NSP can be defined. The


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first is an apparent digestible or metabolizable energy value(DEVa; Eq 22), which is the product of apparent digestibility(fermentability) and heat of combustion. The second is a theo-retical digestible energy value (DEVF; Eq 23) that discountsenergy converted to biomass lost in feces. The third is a theoret-ical net metabolizable energy value (NEVF; Eq 24) that discountsthe remaining losses associated with fermentation. Equation 23assumes that the efficiency of conversion of fermentable carbo-hydrate to fecal bacterial matter is 30% (11, 13, 38) and equation24assumes that the overall efficiency of energy conversion to thesum of fecal bacterial matter, fermentative heat, combustiblegases, and heat associated with inefficient capture of high-energy bonds is 50% (24).

DEVa = DHc 3 D (22)

DEVF = 0.7 3 DHc 3 D (23)

NEVF = 0.5 3 DHc 3 D (24)

Statistics

The feeding trial was examined by analysis of variance(ANOVA; Minitab Inc, State College, PA) using a general linearregression model for 12 dietary treatments representing the basal,starch, and the 10 NSP-supplemented diets. For the analysis oflive weight gain and known quantities (Eq 15), we incorporatedinto the regression model covariance with initial live weight andnet metabolizable energy intake, respectively. Usually, treatmentmeans are given with the RSD or the SEM. Subsequent analysis ofdata in the ANOVA table was undertaken in EXCEL-5 (MicrosoftCorporation, Redmond, WA). We used Dunnett’s test for multiplecomparisons with the basal diet when the ANOVA F ratio wassignificant (39). SBF was given in 4 amounts (including the basaldiet as a zero dose) and a significant dose response was tested byusing linear contrasts for dose (40), and increasing the number ofcontrasts (Dunnett’s a 2 1 means) by 1 for the additional test ofsignificance. Whether the supplements or NSP supplied quantitiesof energy (eg, DEVs and NEVs) different from zero was alsoassessed by using Dunnett’s test because these energy values were

derived as treatment-control difference data in which the controldefined zero. The possibility that a response to one source of NSPwas significantly different from that of all other sources of NSPwas tested by using analysis of contrasts (39) and Dunnett’s criti-cal values for a 2 1 possible sources of NSP. During minimizationbetween equations 17and 18, the significance of a treatment meansuspected to be outlying was tested by obtaining its SD from themean of all the remaining treatment means and comparing thiswith Dunnett’s critical value for a 2 1 means. Limits of agreementbetween the experimental method to determine energy values andmethods using predictive equations, and between experimentallydetermined energy values and equations that summarize them,were obtained by methods comparison analysis, as indicated byAltman (40), for which the limits were equal to the bias plus 2 SDsof difference between methods.

RESULTS

Each carbohydrate source will be considered in turn, begin-ning with the reference sources starch and cellulose, before con-sideration of the results as a whole.

Starch

Starch was used as a reference material with an energy valuecorresponding to full availability (18). Supplementation of thebasal diet with starch (87 g/kg basal diet; Table 1) caused morelive weight gain than did the basal diet (89 compared with 104g/28 d,P< 0.01; Table 3). Nearly all the starch was used in thedigestive tract because its mean (±SEM) apparent digestibilitywas 99± 2% of its intake (Table 4). Although there was a highergross energy intake from the starch-supplemented diet than fromthe basal diet (4254 compared with 3934 kJ/14 d; Table 5), fecalenergy excretion was not significantly higher. The digestibleenergy value of the starch (16.5± 0.4 kJ/g; Table 5) was there-fore similar to its heat of combustion (17.5 kJ/g). The supple-mentation of energy intake with starch increased body fat depo-sition (415 compared with 642 kJ/28 d; Table 6), but this was notsignificant after the multiple comparisons were accounted for.Protein deposition was unchanged by starch supplementation

808 SMITH ET AL

TABLE 3Live weights and live weight gains by rats over 28 d while consuming the basal (B), starch-, and NSP-supplemented diets1

Initial weight Final weight Weight gain Adjusted weight gain2

Diet (RSD = 15, df = 102) (RSD = 17, df = 102) (RSD = 10, df = 102) (RSD = 9, df = 101)

g

B (n = 9) 211 299 89 89B + starch (n = 10) 198 305 1073 1043

B + cellulose (n = 10) 208 297 894 89B + SBF (high) (n = 8) 213 318 104 1043

B + SBF (medium) (n = 10) 212 312 101 1014

B + SBF (low) (n = 9) 207 304 94 94B + hemicellulosic NSP (n = 10) 215 310 96 97B + pectic NSP (n = 9) 209 307 97 98B + cellulosic NSP (n = 10) 219 308 89 92B + whole-beet NSP (n = 10) 211 308 96 97B + fiber K (n = 10) 206 307 101 100B + fiber L (n = 9) 207 301 94 93

1NSP, nonstarch polysaccharide; SBF, sugar beet fiber; RSD, residual SD. Significant dose-response to SBF:P < 0.05 for final weight and weight gain,P < 0.01 for adjusted weight gain. Significantly different n values,P < 0.01.

2Adjusted for initial weight by ANCOVA. Significant difference among diets,P < 0.01 (ANOVA,F ratio test).3,4Significantly different from basal diet [Dunnett’s multiple comparison with basal control (a 2 1 contrasts, including dose = 12)]:3P < 0.01,4P < 0.05.

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(585 compared with 579 kJ/28 d; Table 6). On the basis of pro-tein and fat accretion with supplementary starch intake (Eqs2–18), a significant (P< 0.01 versus m = 0) NEVs value for thestarch supplement was obtained: 16.6± 1.9 kJ/g (Table 6). Thisnet energy value was not different from its digestible energyvalue (Table 7) because the nonfecal supplement-induced energyloss was 0± 2 kJ/g (P> 0.05; Table 6).

Contamination of the starch supplement with other organicmatter was negligible, so the digestible and net metabolizableenergy values estimated for starch were the same as those for thestarch supplement (Table 7). Thus, observations with starch wereprecisely as required for a reference control.

Cellulose

Cellulose was used as a reference material with a gross energythat is unused as either digestible or metabolizable or net metab-olizable energy (15, 18, 25). Supplementation of the basal dietwith the cellulose preparation (92 g NSP/kg basal diet, Table 1)had no effect on body weight gain. Almost no cellulose was usedin the digestive tract because the additional fecal excretion ofunavailable carbohydrate was only 1± 3% of its intake (Table 4).Gross energy intake from the cellulose diet was higher than thatfrom the basal diet alone (4274 compared with 3934 kJ/14 d;Table 4) but the additional energy was matched by a similar ele-vation in the excretion of fecal energy (597 compared with 230kJ/14 d,P< 0.01; Table 5). The cellulose supplement had no

significant influence on either fat (397 compared with 415 kJ/14d) or protein (562 compared with 578 kJ/14 d) deposition (Table6). According to body-composition data, the net metabolizableenergy value of the cellulose supplement (21.7 ± 2.1 kJ/g) wassimilar to its digestible energy value (21.1 ± 0.9 kJ/g); bothwere close to and not significantly different from zero (Table 7).The lack of difference was because the nonfecal cellulose sup-plement–induced energy loss was close to and not significantlydifferent from zero (20.6 ± 2.0 kJ/g; Table 6).

Contamination of the cellulose supplement with other organicmatter and ash was negligible, so the digestible and net metabo-lizable energy values estimated for the cellulose NSP were essen-tially the same as those for the cellulose supplement (Table 7).Thus, observations with the cellulose reference were also pre-cisely as required for a reference control.

Sugar beet fiber

The digestibility and digestible energy value of our SBF prepa-ration are known from interlaboratory trials (15). Hence, this sup-plement added further control to the digestibility and digestibleenergy evaluations, but the efficiency of SBF utilization as anenergy source for maintenance was unknown. The basal diet wassupplemented with 3 amounts of SBF, resulting in 0, 38, 75, and113 g NSP/kg basal diet (Table 1). There were dose-dependentincreases in body weight (89, 94, 101, and 104 g/28 d,P< 0.01;Table 3), gross energy intake (3934, 4113, 4264, and 4443 kJ/14


TABLE 4Fecal excretion of energy, crude protein, fat, carbohydrate by difference, and computation of the apparent digestibilities of the nonstarch polysaccharide(NSP) and starch supplements1

UCf2,3

Diet and supplement FE2,3 Ff2,3 148Nf

2,3,4 Energy Weight5 UCs Md D2,6

kJ kJ kJ kJ g g g, dry g/g

B 2307 31 48 151 8.6 — 199.7 —B + starch 248 398 54 155 8.9 18.4 199.5 0.99 ± 0.029

B + cellulose 5978 428 628 4938 28.2 19.5 199.4 0.00 ± 0.03B + SBF (high) 4738 618 1248 2888 16.5 23.9 199.9 0.67 ± 0.039

B + SBF (medium) 3988 518 998 2488 14.2 15.9 199.4 0.65 ± 0.059

B + SBF (low) 3208 468 778 1978 11.3 8.0 200.2 0.67 ± 0.039

B + hemicellulosic NSP 3188 438 938 1828 10.6 17.7 200.9 0.90 ± 0.049

B + pectic NSP 3438 448 1048 1958 11.1 17.4 197.7 0.85 ± 0.059

B + cellulosic NSP 5168 638 1168 3378 19.3 17.2 193.8 0.37 ± 0.059

B + whole-beet NSP 3668 538 1028 2118 12.1 17.5 197.9 0.80 ± 0.059

B + fiber K 3248 468 948 1848 0.5 17.6 199.4 0.89 ± 0.039

B + fiber L 3048 418 918 172 9.8 17.6 199.5 0.93 ± 0.029

RSD (df: 102) 16 4 7 18 0.091B, basal diet (seeTable 1 for composition); SBF, sugar beet fiber; FE, fecal energy; Ff, fecal fat; Nf, fecal nitrogen; UCf and UCs, unavailable carbohy-

drate in feces and in the supplement; Md, mass of basal diet; D, apparent digestibility; RSD, residual SD.2Significant difference among diets,P < 0.01 (ANOVA F ratio test).3Significant dose-response to SBF,P < 0.01.4Estimates of protein assume 148 kJ/g fecal N; error arising from variation in this value is expected to be limited because the difference data eliminate

errors associated with the basal diet and the conversion is approximately correct for microbial protein; error in D arising from variability in this conversionfactor is less than the variation of the result.

5Conversion to weight assuming 17.5 kJ/g.6x– ± SEM. As an example, the following shows the calculations of D of the supplementary carbohydrate, based on data for the SBF (medium intake) and

B diets (seetext for any undefined terms):UCtf = (FEtf 2 148Ntf 2 Ftf)/17.5 = (398 2 99 2 11)/17.5 = 14.2 g (20)UCcf = (FEcf 2 148Ncf 2 Fcf)/17.5 = (230 2 51 2 48)/17.5 = 8.6 g (20)D = 1 2 [(UCtf/Mtf) 2 (UCcf/Mcd)]/[UCs/Mtd)] = 1 2 [(14.2/199.4) 2 (8.6/199.7)]/[(15.9/199.4)] = 0.65 (19)7x–.8,9Significantly different from basal diet,P < 0.01:8Dunnett’s multiple comparison with basal control (a 2 1 contrasts, including dose = 12),9Dunnett’s

multiple comparison with zero as defined by the basal control (a 2 1 contrasts, including dose = 11).

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d; Table 5), and fecal energy excretion (230, 320, 398, and 473kJ/14 d,P< 0.01; Table 5 and Figure 2). As with cellulose andstarch, the SBF supplement had no significant effect on proteindeposition but the additional digestible energy intake was accom-panied by dose-dependent fat deposition (415, 325, 441, and 619kJ/14 d,P< 0.01; Table 6). By contrast, the excretion of carbohy-drate in feces increased in proportion to the increase in NSPintake so the apparent digestibility of the NSP in SBF was simi-lar for all 3 amounts (67%, 65%, and 67% of intake, Table 4). Foreach amount, nearly one-half of the gross energy (17.4 kJ/g) inthe SBF preparation was available as digestible energy, the DEVs

being independent of amount of intake (9.0, 8.7, and 8.2 kJ/g,P>0.05; Table 5). These digestibility and digestible energy valueswere as expected for the preparation (0.68 g/g and 9.5 kJ/grespectively; 15) and are observations that add to the reliability ofthe present study. The net metabolizable energy value of the SBFpreparation (5.1–9.3 kJ/g) was essentially the same as or less thanits digestible energy value (8.2–9.0 kJ/g; Table 7).

Estimates of the digestible and net metabolizable energy val-ues of the NSP in SBF were slightly lower than the correspond-ing values for the supplement because of the supplement-associ-ated protein, lipid, and lignin (Table 7). Upper and lower errorbounds for these estimates quantified the uncertainty in thederived energy values that arose from uncertainty about theaccompanying protein, lipid, and lignin, but the bounds werewithin 2.0 kJ/g of the estimates made by using the central a pri-ori parameter estimates (from Table 2).

Miscellaneous NSP preparationsA range of NSP preparations other than cellulose and SBF were

used to elevate NSP intake by <83 g/kg basal diet (Table 1). Whenfermented, these preparations generally produced live weight gains.For example, a low live weight gain occurred after consumption ofthe cellulosic preparation (92 compared with 89 g/28 d; Table 3) anda higher gain occurred after consumption of the fiber K preparation(100 compared with 89 g/28 d; Table 3). These gains were associ-ated with low and high apparent digestibilities of the NSP, respec-tively (37% and 89% of intake; Table 4), and low and highdigestible energy values, respectively (5.7 and 10.4 kJ/g; Table 5).The NEVs values of the NSP supplements tended to be less than thecorresponding digestible energy values (Table 7) because of SIELnf

(Table 6). The large SIELnf of 6.8 ± 2.5 kJ/g gave the pectic NSPpreparation a particularly low NEVs value (P< 0.05; Table 6).

Whenever the contaminating protein and fat were just smallproportions of the total amount of supplement, the supplementsand their contained NSPs had similar energy values (Table 7).The adjustments for the quantities of organic contaminants andash in the cellulosic and whole-beet NSP preparations causedappreciably different energy values for the supplements and theircontained NSP and wide error bounds for net energy values,although not for digestible energy values (Table 7).

Diet (energy)-induced energy expenditure

Between animals and within dietary groups, the sum of DITand metabolizable energy for maintenance (MEm) varied linearly

810 SMITH ET AL

TABLE 5Digestible energy balance of animals over 14 d while consuming the basal (B), starch-, and nonstarch polysaccharide (NSP)–supplemented diets andcomputation of the digestible energy value of a supplement (DEVs)

1

DHc DEV2

Gross Ef3,4 Diet or NSP3

energy (RSD = 16, supplement NSP Diet or supplement3 (RSD = 2.9,Diet intake Md df = 102) Ms energy energy (RSD = 2.5, df = 102) df = 102)

kJ g, dry/14 d kJ/14 d g, dry/14 d kJ/g kJ/g NSP

B 39345 199.7 230 ± 36 — 19.7 — 18.57 —B + starch 4254 199.5 248 ± 3 18.4 17.6 (17.5)8 16.69 (16.5 ± 0.4)6,8,9

B + cellulose 4274 199.4 597 ± 610 19.5 17.7 17.5 21.1 21.3 ± 0.9B + SBF (high) 4443 199.9 473 ± 610 29.1 17.4 17.1 9.09 7.9 ± 0.69

B + SBF (medium) 4264 199.4 398 ± 810 19.3 17.4 17.1 8.79 7.4 ± 1.29

B + SBF (low) 4113 200.2 320 ± 310 9.7 17.4 17.1 8.29 6.8 ± 1.19

B + hemicellulosic NSP 4265 200.9 318 ± 710 17.7 17.3 16.3 12.49 11.5 ± 1.29

B + pectic NSP 4191 197.7 343 ± 710 19.9 14.9 15.6 9.29 9.1 ± 1.09

B + cellulosic NSP 4248 193.8 516 ± 610 24.0 17.9 18.6 5.79 2.9 ± 0.99

B + whole-beet NSP 4261 197.9 366 ± 610 20.1 18.0 17.2 11.29 10.7 ± 0.99

B + fiber K 4215 199.4 324 ± 310 18.5 15.5 15.6 10.49 10.3 ± 0.59

B + fiber L 4221 199.5 304 ± 210 19.6 14.9 15.6 11.19 11.5 ± 0.59

1SBF, sugar beet fiber; Md and Ms, mass of basal diet eaten and of supplement; Ef, fecal energy; DHc, heat of combustion; RSD, residual SD.2As an example, the following shows the calculation of the DEVs, based on data for the SBF (medium) and basal diets:DEVs = ∆Hc 2 {[( Etf/Mtd) 2 (Ecf/Mcd)]/(Ms/Mtd)} = 17.4 2 {[(398/199.4) 2 (230/199.7)]/(19.3/199.4)} = 8.7 kJ/g (1)Computation of DEVNSP from DEVs was according to Eq 16 and the a priori parameter estimates in Table 2.3Significant differences among diets,P < 0.01 (ANOVA F ratio test).4Significant dose response to SBF,P < 0.01.5x–.6x– ± SEM.7SEM = 0.02 kJ/g.8For comparison with NSP, the value for starch is included in parentheses and has units of kJ/g starch.9,10Significantly different from basal diet,P < 0.01: 9Dunnett’s multiple comparison with basal control (a 2 1 contrasts, including dose = 12),

10Dunnett’s multiple comparison with zero as defined by the basal control (a 2 1 contrasts, including dose = 11).

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with net metabolizable energy intake per unit average lean mass(Figure 3; upper panel). This relation was unperturbed by theelevation in energy intake, as was achieved with the starch sup-plement. Individual data from animals consuming the NSP sup-plements fit the same regression line (Figure 3; lower panel), aline that indicated that the mean (±SD) DIT was 0.51± 0.06kJ/kJ NME when calculated by using the central a priori param-eter estimates. The a priori estimates gave error bounds for DITof 0.38 and 0.63 kJ/kJ NME, almost entirely because of the

potential variation in the energy costs of fat and protein deposi-tion (Table 2).

Solving f, the efficiency of digestible energy utilizationfrom NSP, for net metabolizable energy

The efficiency value was obtained by finding the value of fthat minimized differences in the results of equations 17 and 18.Information for the pectic NSP preparation was excludedbecause its mean treatment value was outlying, being 3.3 SDs


TABLE 6Net energy balance of animals over 28 d while consuming the basal (B), starch-, and nonstarch polysaccharide (NSP)–supplemented diets andcomputation of net metabolizable energy (NEVs) value of the supplement1

EP EF2 AL (KQ/AL) at DIT = 0 SIELnf/Is3 NEVs

3,4,5

(RSD = 87, (RSD = 227, (RSD = 3.1, (RSD = 4.8, (RSD = 6.1, (RSD = 6.7,Diet and supplement Mb Is DE NME df = 102) df = 102) df = 102) df = 102) df = 102) df = 102)

g, dry/28 d g, dry/28 d kJ/28 d kJ/28 d kJ/28 d kJ/28 d g kJ/g 4L kJ/gIs kJ/gIs

B 400 — 73916 6815 579 415 58.8 95.0 — —B + starch 394 36.8 7889 7322 585 642 56.3 95.0 0.0 ± 1.87 16.6 ± 1.98

B + cellulose 396 39.1 7273 6718 562 397 57.9 95.4 0.6 ± 2.0 21.7 ± 2.0B + SBF (high) 394 58.1 7819 7095 571 619 59.9 94.7 20.2 ± 1.8 9.3 ± 2.18

B + SBF (medium) 395 38.7 7644 6975 598 441 59.6 96.1 1.7 ± .8 7.0 ± 3.09

B + SBF (low) 398 19.4 7528 6906 630 325 59.8 96.0 3.1 ± 2.8 5.1 ± 2.2B + hemicellulosic NSP 389 35.5 7802 7089 614 408 60.7 97.2 3.9 ± 1.8 8.5 ± 3.08

B + pectic NSP 381 39.8 7558 6888 571 326 58.7 99.6 6.8 ± 2.5 2.3 ± 2.2B + cellulosic NSP 390 48.0 7326 6700 616 333 60.5 94.4 20.8 ± 1.8 6.5 ± 2.09

B + whole-beet NSP 390 40.2 7665 6962 612 348 59.8 98.5 5.3 ± 2.0 5.9 ± 2.2B + Fiber K 393 37.0 7664 6982 584 540 58.3 95.4 0.6 ± 2.4 9.8 ± 2.58

B + Fiber L 395 39.1 7752 7052 599 478 58.7 96.9 2.9 ± 1.6 8.2 ± 1.78

1SBF, sugar beet fiber; Mb, mass of basal diet eaten; Is, mass of supplement eaten; DE, digestible energy intake; NME, net metabolizable energy intake(estimated); EP, lean gain; EF, fat gain; AL, average lean mass; SIELnf, nonfecal supplement-induced energy loss; KQ, known quantity; DIT, diet-inducedthermogenesis; RSD, residual SD.

2,5Significant dose response to SBF:2P < 0.05,5P < 0.01.3Significant differences among supplements,P < 0.01 (ANOVA F ratio test).4As an example, the following shows the calculation of the NEVs of SBF (medium dose). Data are given to at least the first nonsignificant figure to avoid

rounding errors (seetext for terms not defined here):DE = (Mb 3 DEVbasal) + (Is 3 DEVd ) (3)Basal diet = (399.5 3 18.5) + (0 3 0) = 7391SBF = (395.0 3 18.5) + (38.7 3 8.69) = 7644NMEdiet = Mb 3 DEVb + Is 3 DEVs (14)

2 Mb (7.2 3 Ppr + 1.8 3 Pfat)b

2 Is (7.2Ppr + 1.8Pfat + 6.6Plg + (1 2 f)DEVNSP 3 PNSP)s

Basal diet = 399.5 3 18.5 + 0 3 02 399.5 (7.2 3 0.179 + 1.8 3 0.0851)b2 0 (0)s = 6815

SBF = 395.0 3 18.5 + 38.7 3 8.692 395.0 (7.2 3 0.179 + 1.8 3 0.0851)b2 38.7 (7.2 3 0.089 + 1.8 3 0.038 + (1 2 0.71)7.43 3 0.87) = 6975

From equation 6 divided by AL:(KQ/AL) = (DE 2 1.36EF 2 2.25EP)/ALBasal diet = (7391 2 1.36 3 414.6 2 2.25 3 578.7)/58.8 = 94.0SBF = (7644 2 1.36 3 441.2 2 2.25 3 597.5)/59.6 = 95.6

By rearrangement of equation 15:(KQ/AL)DIT = 0 = KQ/AL 2 bDIT 3 [(NME/AL) td 2 (NME/AL)exp mean]Basal diet = 94.0 2 0.51 3 [(6815/58.8) 2 (117.9)] = 94.0 2 (21.02) = 95.0SBF = 95.6 2 0.51 3 [(6975/59.6) 2 (117.9)] = 95.6 2 (20.44) = 96.1(SIELnf/AL) t = [(KQ/AL) td 2 (KQ/AL)cd]DIT = 0 = 96.1 2 95.0 = 1.4 (11)(SIELnf/ Is)t = (SIELnf/AL) t/(Is/AL) = 1.1/(38.7/59.6) = 1.69 (12)NEVs = DEVs 2 SIELnf = 8.69 2 1.69 = 7.0 kJ supplement/g supplement dry matter (2)

6x–.7x– ± SEM.8,9Significantly different from zero [Dunnett’s multiple comparison with zero as defined by the basal control (a 2 1 contrasts, including dose = 11)]:8P

< 0.01,9P < 0.05 [Note that NEVs = DEVs 2 SIELnf/Is (Eq 2) and a lack of significant dose response for both DEVs (Table 5) and SIELnf/Is (above)].

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from the mean difference between the results of equations 17and18 for the remaining NSP preparations. The mean of absolutedifferences varied with variation in f, both when using the cen-tral a priori parameter estimates and their upper and lower errorbounds (Figure 4). The absolute difference reached a minimumat f = 0.71 with an SE of 0.07 and error bounds at 0.58 and 0.79kJ NEVNSP/kJ DEVNSP. The minima for the error bounds did notreach as low as those for the central a priori parameter estimates,making these error bounds less probable. The resulting relationbetween NEVNSP and DEVNSP, with slope f = 0.71, is shown inFigure 5. This figure also includes the error bounds for the rela-tion and the theoretical slope (NEVNSP = 0.68 3 DEVNSP) sug-gested previously (15). Observed NEVNSP values were in goodagreement with those predicted from theory, with a mean differ-ence of just 0.5± 0.5 kJ/g (lower bound 0.5 and upper bound 0.7kJ/g). The limit of agreement for future predictions betweenthose observed and those predicted (ie, the absolute bias + 2 SDof fit) was 3.8 kJ/g (error bounds: 3.5, 4.7 kJ/g).

The pectic NSP mean was outlying, but no individual pecticNSP data points deviated unusually from either the group meanor the experimental mean adjusted for groups (Figure 3). Theerror term for the pectic SIELnf value was not large relative toeither other treatments or to the pectic NSP mean value (Table6). Nonpectic NSP data were used to derive f, and comparisonof NEVNSP values given by equations 17 and 18 after minimiza-

tion showed a difference of just 20.3 kJ/g with a deviation (SD,n = 9 treatment means) of 1.6 kJ/g. The deviation for the pecticpreparation was larger (5.4 kJ/g), with an SD from the mean ofall other NSP treatments of 3.30 kJ/g. Dunnett’s critical valueapplied to this circumstance, to avoid selection error, was 3.29(table parameters: two-tailed,2a = 0.05, df = 8,a 2 1 con-trasts = 7, where a was 10 NSP treatments minus 2 because 3treatments were the same SBF source). Thus, with central a pri-ori parameter estimates, the pectic NSP value was outlying withP > 0.05. With a priori parameter estimates at the upper andlower bounds, the significance dropped to P< 0.1. The efficiencyof use of DEVNSP from the pectic NSP for NEVNSP is consideredin more detail in a subsequent section.

Do the present data validate prior linear models relatingenergy values and fermentability of NSP?

For practical reasons and simplicity, linear interpretations ofrelations between energy and fermentability would be valuable.Digestible energy values did approximately fit a linear trend withNSP fermentability (Figure 6). The figure shows the individualvalues that were obtained, both for the whole supplements(DEVs) and for their contained NSP (DEVNSP). The precisedigestible energy values for the NSP depended on the energy val-ues of the contaminants, so we also show the upper and lowererror bounds for these estimates. The error bounds (bars parallel

812 SMITH ET AL

TABLE 7Calculated energy values of the supplements and their contained nonstarch polysaccharides (NSP) with error bounds1

DEV NEVSupplement energy2 NSP energy2 Supplement energy2.3 NSP energy2.3

∆Hc (RSD = 2.5, (RSD = 2.9, (RSD = 6.7, (RSD = 7.9,Supplement Supplement energy NSP energy df = 102) df = 102) df = 102) df = 102)

kJ/g kJ/g NSP kJ/g kJ/g NSP kJ/g kJ/g NSP

Starch 17.64 [17.5 (17.5, 17.5)]5,6 16.67 [16.57 (16.5, 16.6)]6 16.67 [16.47 (16.5, 16.6)]6

Cellulose 17.7 17.5 (17.5, 17.5) 21.1 21.3 (21.3,21.3) 21.7 21.9 (22.1,21.6)SBF

High 17.4 17.1 (16.7, 17.5) 9.07 7.97 (7.0, 9.2) 9.37 8.28 (6.1, 9.9)Medium 17.4 17.1 (16.7, 17.5) 8.77 7.47 (6.6, 8.8) 7.08 5.4 (3.6, 7.1)Low 17.4 17.1 (16.7, 17.5) 8.27 6.87 (6.0, 8.2) 5.1 3.1 (0.8, 5.5)

Hemicellulosic NSP 17.3 16.3 (16.2, 16.4) 12.47 11.57 (11.3, 11.9) 8.57 7.78 (6.3, 7.9)Pectic NSP 14.9 15.6 (15.5, 15.7) 9.27 9.17 (8.8, 9.6) 2.3 1.3 (0.3, 1.3)Cellulosic NSP 17.9 18.6 (18.0, 19.2) 5.77 2.97 (1.6, 5.1) 6.58 4.0 (1.3, 7.6)Whole-beet NSP 18.0 17.2 (17.1, 17.3) 11.27 9.87 (9.4, 10.4) 5.9 5.6 (3.8, 4.8)Fiber K 15.5 15.6 (15.5, 15.6) 10.47 10.37 (10.2, 10.5) 9.87 9.77 (8.1, 10.1)Fiber L 14.9 15.6 (15.6, 15.7) 11.17 11.57 (11.3, 11.8) 8.27 8.37 (6.9, 8.5)

1SBF, sugar beet fiber; DHc, heat of combustion; DEV, digestible energy value; NEV, net metabolizable energy value; RSD, residual SD. As an exampleof estimation of values per g NSP from values per g supplement (Eq 16), the following calculation is given for data on the “high” SBF preparation. In thefollowing formulas,DHc, DEV, and NEV are energy values with units of kJ/g dry organic matter (OM) and P is proportion of supplement (g/g dry OM).Input data were therefore first converted from values per g dry matter (DM) to values per g dry OM such that the value per g OM =value per g DM/(1 2ash), where ash was in units of g per g dry supplement. Seetext for any terms not defined.

From Table 3: DHc SBF preparation = 17.4 kJ/g DME (kJ NSP/g NSP) = [(Es 2 (Epr 3 Ppr) 2 (Elg 3 Plg ) 2 (El 3 Pl)]/PNSP (16)or [17.4 2 (23.6 3 0.088) 2 (35 3 0.019) 2 39.3 3 0.014]/0.824 = 17.1 kJ NSP/g NSP

DHc, DEV, and NEV values of protein (pr), lignin (lg), and lipid (l) used in these calculations are from Table 2.2Significant differences among supplements,P < 0.01 (ANOVA F ratio test).3Significant dose response to SBF,P < 0.01.4Calculated value.5Calculated value with upper and lower error bounds in parentheses.6For comparison with NSP, the value for starch is included in square brackets and has units of kJ/g starch.7,8Significantly different from zero [Dunnett’s multiple comparison with zero as defined by the basal control (a 2 1 contrasts, including dose = 11)]:7P

< 0.01,8P < 0.05.

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to the y axis in Figure 6) were not large, indicating that contam-ination did not introduce a critical source of uncertainty. Simi-larly, error bounds for the fermentability of NSP (shown parallelto the x axis in Figure 6) were sufficiently small to not criticallyaffect the trend. One curve in Figure 6 shows the trendDEVNSP = 0.7 3 D 3 17.2 that was suggested previously (1, 15),and with which the data agreed. Indeed, fitting the data to such atrend gave DEVNSP = 0.67 (SEM: 0.03) 3 D 3 17.2 kJ/g; theassociated error bounds were 0.60 and 0.77. The present obser-vations therefore validate the model suggested previously. Themean difference between the predicted trend (of slope 0.7) andobserved energy values was only 20.5 ± 0.3 kJ/g (lower andupper error bounds:21.2 and 0.8 kJ/g). The limits of agreementfor future predictions (absolute bias +2 SD of fit) betweenobserved and predicted values (with slope 0.7) was 2.0 kJ/g(error bounds: 2.7 and 2.7 kJ/g). Thus, we can confidently expectpredictions to be within 3 kJ/g when fermentability is used topredict the digestible energy value, given fermentability deter-mination of the present degree of accuracy.

The net energy values of the NSP preparations and their con-tained NSP also varied with the fermentability of the NSP, withthe exception of the pectic preparation and its NSP (most outly-ing value to the lower left in Figure 7). A line in Figure 7 showsthe linear trend, NEVNSP= 0.5 3 D 3 17.2, suggested previously(25). Fitting the data (except that for the pectic NSP) to such amodel gave NEVNSP = 0.51 (SEM: 0.03) 3 D 3 17.2 kJ/g; theerror bounds were wide (0.37 and 0.63 kJ/g). The mean (±SEM)difference between observed and predicted energy values was20.1 ± 0.6 kJ/g (lower bound and upper bounds:21.8 and 1.5kJ/g). The limit of agreement for future predictions between thepredicted trend and the observed values was 3.5 kJ/g (errorbounds: 5.2 and 5.8 kJ/g). Thus, the previously suggested rela-tion (25) was valid with central a priori parameter estimates.

Nonlinear energy losses from NSP in relation tofermentability

Although linear trends may offer a practical, simple summaryof the results (as above), nonlinearity is a realistic possibility.The fractional loss of NSP gross energy in feces was calculated

[ie, (DHc 2 DEVNSP)/DHc; kJ/kJ DHc] and this increased withnonfermentability (1 2 d; kJ/kJ DHc) of the NSP, as shown inFigure 8. An attribute of this plot is that both x and y axes haveDHc as the denominator, which minimizes the error due to pos-sible errors in the estimation of this quantity. The curve inter-cepted the y axis at 0.08 (error bounds: 0.04, 0.10) and the slopefit a power term [(1 2 d)0.66] (error bounds for the power coef-ficient: 0.60, 0.74). Deduction of the energy losses [0.08 + (1 2d)0.66] from 1 gave the fractional digestible energy gain, whichwhen multiplied by the heat of combustion gave the digestibleenergy value: DEVNSP = DHc 3 (1 2 [0.08 + (1 2 d)0.66]). Thedata fit this power relation with an RSD of 0.03 kJ/kJ NSPintake or 0.5 kJ/g NSP. Given that in Figure 8, the fractionalenergy losses to feces as unfermented NSP rose by definitionwith unit slope, the nonlinear fit must result from variation inthe conversion of fermentable NSP gross energy to non-NSPenergy (biomass), which rose then fell with increasing nonfer-mentability of the NSP.

The total energy loss from NSP, expressed as a fraction ofNSP gross energy intake [ie, (DHc 2 NEVNSP)/DHc; kJ/kJ DHc],similarly fit the nonlinear curve described above after a linearcomponent for nonfecal energy losses equal to 0.18d was added(error bounds: 0.16, 0.27), as found by least squares fitting. Con-sequently, the net metabolizable energy value of the NSP fit thefollowing equation: NEVNSP = DHc 3 (1 2 [0.08 + (12 d)0.66 +


FIGURE 2. Fecal energy excretion (Ef) by individual rats with con-sumption of increasing amounts of sugar beet fiber (Is) after normaliza-tion for the mass of basal diet eaten (Md).

FIGURE 3. Covariance between metabolizable energy for mainte-nance plus diet (energy)-induced thermogenesis (MEm + DIT) and netmetabolizable energy intake (NME). AL, average lean dry mass. Upperpanel: control and reference data, which are for rats consuming the basaldiet alone (s) and the basal diet supplemented with cellulose (D) orstarch (h). Lower panel: the basal diet supplemented with low-dosesugar beet fiber (SBF) (filled symbols); j, medium-dose SBF; m, high-dose SBF; d, hemicellulosic nonstarch polysaccharide (NSP);m, pecticNSP; j, cellulosic NSP; s, whole-beet NSP; h, fiber K; D, fiber L.

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814 SMITH ET AL

0.18d]) as shown in Figure 8. Data fit this curve with a smallRSD of 0.09 kJ/kJ NSP intake or 1.6 kJ/g NSP, indicating thenonlinear equation to be a reasonable summary of the results.

Substrate-induced energy expenditure

Evidence for or against NSP-induced energy expenditure inexcess of DIT and fermentation-related heat energy losses wasobtained from the present data in several ways, but all except the

pectic NSP preparation suggested that, in general, NSP did notinduce such a response. First, the lower curve in the lower panelof Figure 8 fit a slope of 0.18d; this means that 18% of the fer-mentable energy in NSP was liberated as heat and combustiblegases, which is similar to the theoretical value of 20% (25). Val-ues >20% provide evidence of NSP-induced energy expenditure,but this was 22 ± 4% and corresponds to just 20.3± 0.6 kJ/g fora fully fermentable NSP. Second, in Figure 7, NEVNSP was equalto 0.51 ± 0.03 times the fermentable energy in NSP (ie,D 3DHc). This means that 51% of fermentable energy was availableto meet energy requirements, compared with a theoretical valueof 50% (24). Values <50% provide evidence of NSP-inducedenergy expenditure, but this was 21 ± 3% and corresponded tojust 20.2 ± 0.6 kJ/g for a fully fermentable NSP. Third, moredirect evidence comes from Figure 5 in which the experimentalvalue of f was 0.71, which means that 71% of DEVNSP usefullymet energy requirements, similar to a theoretical value of 68%.Values <68% provide evidence of NSP-induced energy expendi-ture, but this was 23 ± 7% of the digestible energy from NSP andcorresponded to just 20.3± 0.6 kJ/g for a fully fermentable NSP.

Although NSP was generally no more thermogenic thanexpected on theoretical grounds (Figures 5, 7, and 8), the obser-vation for pectic NSP was outlying, which suggested that thissource of NSP was potentially thermogenic. Values of NEVNSP

<0.71DEVNSP (data from Table 7) indicate possible NSP-induced energy expenditure. Compared with zero (defined bythe basal treatment), the thermic response to pectic NSP was5.1 ± 2.3 kJ/g and barely significant at P< 0.1 (Dunnett’s test).The size of the response was, nevertheless, appreciable becauseit corresponded to 33± 15% of the heat of combustion of thepectic NSP (error bounds: 32%, 42%). A question that could betested more powerfully was whether the pectic NSP was ther-mogenic compared with all other sources of NSP. A one-tailedtest would normally be sufficient for such a question askedprospectively, but because the question was asked retrospec-tively, a two-tailed test was required. Thus, analysis of contrastsfor the pectic NSP treatment compared with all others (ie, 7 3pectic NSP deviation 2 S deviation for each of 7 other NSPtreatments) indicated a difference of 5.4± 1.8 kJ/g, significant

FIGURE 4. Theta (f), the efficiency with which the digestibleenergy value of nonstarch polysaccharide (DEVNSP) can be used for thenet metabolizable energy value of NSP (NEVNSP), estimated by mini-mization. Theta is given by the lowest point on any curve. The boldcurve was calculated by using the central a priori parameter estimatesand the 2 other curves by using the upper and lower error bounds (Table2). Each curve shows the difference in results between equations 17 and18, expressed per unit weight of NSP.

FIGURE 5. Prediction of the net metabolizable energy value of nonstarch polysaccharide (NEVNSP) from the digestible energy value of NSP(DEVNSP). Data points are mean values for the treatments, determined by using central a priori parameter estimates. The broken line shows the rela-tion suggested previously (25) with slope 0.68, and the solid lines show the slope of the regression line for the data points shown, 0.71, together withthe upper and lower error bounds for the regression line.

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at the P< 0.05 level (Dunnett’s two-tailed test, df = 102,a 2 1 = 7for the number of NSP sources possible to select minus one).Thus, the pectic NSP was thermogenic when assessed by usingcentral a priori parameter estimates with a 5% error rate; whenusing upper and lower bounds for the a priori parameter estimateswe obtained significance values of P< 0.01 and P< 0.1, respec-tively. These results agree with the test for outlying means againstthe distribution of all remaining means (seesection on f above).

Overall, we found a thermic response for the pectic NSP prepa-ration above that caused by DIT or associated with fermentationand inefficient metabolism of fermentation products, but thisresponse was significant only within a 10% error rate (ie,P< 0.1),this being the highest rate reached within the confines of the errorbounds for the a priori parameter estimates.

DISCUSSION

Expert committees (10, 21, 41) and researchers (22–25, 42)have assumed that carbohydrates that undergo fermentation in thelarge intestine cause thermic responses no greater than have beenpredicted on theoretical grounds. However, information on theefficiency with which systemic metabolism uses NSP for energy isscant. Theory predicts thermogenesis associated with NSP to bethe sum of the heat of fermentation in the large intestine and theheat produced from the end products of fermentation, short-chainfatty acids, in excess of that from glucose for the same recovery ofhigh-energy bonds (10, 21–25, 42, 43). These total <20% of thegross energy in carbohydrate that undergoes fermentation. Ahypothesis that the prediction is correct appears to be refuted byobservations of guar gum, a fermentable NSP that is thermogenicin rats (17, 18). Similarly,D-tagatose, a rare sugar that undergoesfermentation, appears to elicit a thermic response (19). Whethersuch thermogenesis is an important general response to fer-mentable NSP intake is a question that appears to have remainedunanswered before now, possibly because such studies are difficultto perform; they need to be tightly controlled, detailed in their per-formance and data analysis, and meticulously executed.

Experimental control was achieved in this study by using the

substrates cellulose and starch, which are known to be unavail-able and fully available energy sources, respectively. Thedigestible and net metabolizable energy values of both controlsubstrates were close to values expected from previous studieswith cellulose (18, 27) and starch (18). In addition, the digestibleenergy value of the SBF preparation obtained was close toexpectations from previous work (15). Furthermore, the apparentdigestibilities (D) or fermentabilities of these 3 substrates were99%, 0%, and 67% compared with 99%, 7%, and 68% in previ-ous studies (15, 18), respectively. The close correspondencebetween the values obtained and prior values for these materialsgave confidence that reasonable control was established in thisstudy. For cellulose and SBF, the previous estimates of fer-mentability were obtained by using direct measures of NSP infood and feces; thus, the close correspondence was not simplybecause of good reproducibility but also indicated that our by-difference approach to estimating fecal carbohydrate (Eq 20)was reasonably good in this case. In addition, the causes ofuncertainty in the present work were addressed directly by con-siderating the error bounds. For digestible energy and fer-mentability, the error bounds were sufficiently small (Figure 6)to consider the results reasonably precise. For net metabolizableenergy values, the error bounds were sometimes large (Figure 7)and so the conclusions were less precise.

Some consideration needs to be given to the calculation modelused—in particular, its response to possible errors in the a prioriestimates of the energy costs of fat and protein deposition and inthe model’s response to changes in physical activity of the ani-mals. Although the energy cost values adopted (Eqs 4–6 ) arewidely applicable (18, 20, 30), they may not fit a particular exper-iment precisely. Fortunately, the consequences of deviation fromthe values used was restricted largely to change in the outcomecalculated for DIT, and had only a small influence on the estimateof nonfecal supplement-induced thermogenesis and thereforeNEVs (Table 7). The DIT in the present study contrasts with itsabsence when ambient temperature is thermal neutral for rats(18). This required us to revisit and elaborate our calculationmodel and derivation of formulas for the determination of net


FIGURE 6. Prediction of the digestible energy value (DEV) of dietary fiber preparations and of the nonstarch polysaccharide (NSP) they containbased on values of D, the fermentability of NSP. Open squares show values for the supplements; closed squares show values for the NSP contained inthe supplements when estimated by using the central a priori parameter estimates. The vertical bars show the upper and lower error bounds of DEVNSP

estimated by using the upper and lower error bounds of the a priori parameter estimates. Similarly, the horizontal bars show the upper and lower errorbounds of fermentability.

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816 SMITH ET AL

metabolizable energy values. The derivation made use of ascheme (Figure 1) that describes the components of energy bal-ance and how energy is used in animals. Unlike a previous exper-imental approach of ours that involved calorimetry and physicalactivity measurements (44), the present approach cannot directlyaccount for energy expended on physical (or behavioral) activity.It is sometimes claimed that rats kept at temperatures below ther-mal neutral, with restricted amounts of food, and confined to acage spend little energy on physical activity; however, this is notso because as much as 20% of a rat’s energy expenditure can berelated to physical activity under these conditions (44). It is there-fore useful to consider how the present calculation model isexpected to respond to changes in physical activity.

The method we used to calculate the net metabolizable energyvalue makes no assumptions about the physical activity of theanimals. It is obvious, however, that a dietary supplement thatcauses increased physical activity compared with an isoenergeticcontrol diet will raise the SIELnf value to one above that expectedtheoretically. Should this occur, the calculated net metabolizableenergy value would then be below that expected on theoreticalgrounds. Alteration in physical activity with a supplement istherefore a hypothetical mechanism to explain supplement-induced thermogenesis when it occurs. Except for the pecticNSP preparation (seebelow), we observed no such supplement-induced thermogenesis with any of the NSP preparations. Thus,the thermic response to NSP preparations is generally pre-dictable. There is, therefore, no NSP-induced thermogenesis toexplain and so no need to implicate physical activity or any puta-tive thermogenic mechanism activated by NSP per se in ourresults (18). Although an absence of significant supplement-induced thermogenesis appeared to be the norm, those supple-ments that supplied net metabolizable energy also caused DIT.The cause of such DIT cannot be identified from the present dataand a progressive release from behavioral energy conservationwith increasing energy intake is a possibility (44).

The absence of supplement-induced thermogenesis in the gen-eral case needs to be put into context both quantitatively andcomparatively with previous observations on guar gum. Thus,

the average supplement-induced thermic response was20.3 ± 0.6 kJ/g NSP supplement, which is negligible because itcorresponds to only 2% of the heat of combustion of NSP, and<24% of the average digestible energy from NSP. This valuecontrasts markedly with guar gum (18), for which the supple-ment-induced thermogenesis (12–15 kJ/g) is close to or >100%of the gum’s digestible energy (10 kJ/g) when present in a basaldiet of the same composition as in this study. Interestingly, thepectic NSP preparation appears to cause supplement-inducedenergy expenditure (see Results section on substrate-inducedenergy expenditure) by 33% of its heat of combustion and 57%of its digestible energy value. The similarity of results for guargum and pectic NSP may be more than coincidental because theyshare similar physical properties of viscosity in solution andgelation at higher concentrations (45).

The general case of an absence of NSP-induced thermogene-sis, beyond what is predictable, leads to the suggestion that NSPper se, whether fermentable or not, has only moderate influenceon whole-body energy requirements. The remodeling of the gas-trointestinal tract that occurs to accommodate exposure to ele-vated NSP intake has been suggested as a cause of thermogenesiswith guar gum (18). However, the present data suggest that theoverall energy cost of such remodeling and maintenance of thegastrointestinal tract structure and activity after ingestion of NSPper se must generally be negligible in the context of whole-bodyenergy expenditure. Thus, some other explanation is required inthe case of guar gum (18) and the pectic NSP in our study, but itis not possible to identify the cause from either the present dataor from the list of possibilities described previously (18).

Several quantitative interrelations were proposed previously,and the present data allow the reliability of such relations to betested. First, a prior linear model predicts the digestible energyvalue of NSP based on knowledge of the fermentability of NSP(11, 15) such that DEVNSP = 0.7 3 D 3 17.2 (compare with Eq22). The coefficient of 0.7 in this model is similar to our estimateof 0.67± 0.03, suggesting both that the prior model is reasonablygood and that the proportion of fermentable energy that is generally lost to feces is on average close to (1 2 0.67) or 0.33,

FIGURE 7. Prediction of the net metabolizable energy value (NEV) of dietary fiber preparations and of the nonstarch polysaccharide (NSP) theycontain based on values of D, the fermentability of NSP. Open squares show values for the supplements; closed squares show values for the NSP con-tained in the supplements when estimated by using the central a priori parameter estimates. The vertical bars show the upper and lower error boundsof the digestible energy value of NSP (DEVNSP) estimated by using the upper and lower error bounds of the a priori parameter estimates. Similarly, thehorizontal bars show the upper and lower error bounds of fermentability.

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or 33% of the carbohydrate fermented. Second, digestible energyconverts to net metabolizable energy such that NEVNSP = 0.68 3DEVNSP (15), and the coefficient in this equation is similar to thevalue we determined for f of 0.71± 0.07. Third, fermentabilityis considered to convert to net metabolizable energy such thatNEVNSP = 0.5 3 D 3 DHc (25). The coefficient in this equationis similar to the value we obtained, 0.51± 0.03, a value that sug-gests that an energy equivalent of 196 (ie, 100/0.51) kJ fer-mentable carbohydrate supplies the same amount of high-energybonds to fuel metabolism as does 100 kJ fully available glucose.In general, all of these values met with prior expectations; how-ever, never before have they been so rigorously tested and neverhave the results been derived for NSP in supplements—the pres-ence of contaminating substances was ignored previously. This isthe first time that theory has been tested for NSP with regard toestimation of the values of NEVs and the first time an experi-mental estimate has been obtained for f. These relations assumelinearity between fermentability, digestible energy value, and netmetabolizable energy value. For practical purposes, this seemed

acceptable because deviation from linearity was not great. Nev-ertheless, there was evidence of nonlinearity, which we attrib-uted to variation in the efficiency of conversion of fermentableNSP to non-NSP fecal energy.

Several conclusions can be drawn from the present study.First, under conditions in which DIT is evident, fermentable NSPsupplies energy that induces such a thermic response. Second,apart from DIT, there is in general no novel thermic responsewith either highly fermentable or poorly fermentable NSP thathas a significant effect on energy balance at realistic NSPintakes. Third, in general the fermentability, digestible energyvalue, and net metabolizable energy value of an NSP product areclosely interrelated. Fourth, certain NSP products, like guar gum(18), cause a thermogenic response independent of DIT and ourpectic NSP appears to be such a material, but there was a con-siderably smaller response to the pectic NSP than to guar gum.Fifth, the ability of fully fermentable NSP to meet 100 kJ ofenergy requirements can be compared with published values (5, 6) for protein, fat, and glucose and is 196 compared with 128,

FIGURE 8. Nonlinear interpretation of energy losses from nonstarch polysaccharide (NSP). Upper panel: Closed symbols show total fecal energylosses from the supplemental NSP and the corresponding nonlinear regression line (solid) calculated by using the central a priori parameter estimates;the associated broken lines show the upper and lower error bounds. The line with unit slope shows, by definition, the energy loss from NSP as NSP infeces. Open symbols show fecal energy loss from NSP as combustible matter other than NSP (ie, biomass) and the associated curves calculated withcentral, upper, and lower a priori parameter estimates. Lower panel: Closed symbols show the total of all energy losses from the supplemental NSP andthe nonlinear regression line (solid) calculated by using the central a priori parameter estimates; the associated broken lines show the upper and lowererror bounds. Open symbols and the associated curves show NSP-induced nonfecal energy loss from NSP (ie, the sum of the heat of fermentation, heatloss due to inefficient capture of energy from NSP as high-energy bonds, and any supplement-induced energy expenditure) calculated with central,upper, and lower a priori parameter estimates.

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105, and 100 kJ apparent metabolizable energy, respectively,where apparent metabolizable energy means gross energy timesmetabolizability (or fermentability in the case of NSP). Finally,considering the evolutionary conservation in the efficiency ofenergy utilization across species (20), we should not expect anynegative energy balances associated with increased NSP intaketo be due to any putative NSP-induced thermogenesis in humanseither. Without alterations in food intake, the influences of NSPon energy balance and health related to body weight are, there-fore, probably no more than we predicted previously by usingactuarial statistics and energy balance data at various unavailablecarbohydrate intakes (46, 47).

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