protein in exercise

NDD 30503

LECTURE 4Protein in Exercise

DR. SHARIFAH WAJIHAH WAFA BTE SST WAFA & HH02

WEDNESDAY (27 SEPTEMBER 2017), 3:00-5:00PM

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Functions of Proteins

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Enzymes

Hormones

Structural

Immunologic

Transport and storage

pH buffering

Energy source


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Structure of Proteins

• Proteins are made of individual “building block” units called

________ that are linked together

– A chain of AAs is called a _______

– Long peptides are ______

• The order of the AAs allows different proteins to have

different functions

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What Are Amino Acids?

• Building blocks of proteins– Body uses 20 different amino acids to make proteins

• ____ of the 20 amino acids must be consumed in the diet (essential amino acids; EAA)

• Other ___amino acids are not essential (NEAA)

• Some NEAAs can become EAAs under certain conditions– Infants have different needs for growth

– Defects in amino acid metabolism• Tyrosine can become essential in individuals with

phenylketonuria (PKU), an inborn error of phenylalanine metabolism

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Basic Structure of an

Amino Acid

• Central carbon atom (alpha carbon [Cα])

linked to

– Amino group (positive)

– Carboxylic acid group (negative)

– Hydrogen

– Distinctive side chain (R)

• Makes each AA different

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+–


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R Groups for Some Amino Acids

H-

CH3-

H3C

H3C

CH-

H3C

H3C

CH-CH2-

CH2

CH2

CH-

CH3

Glycine

Alanine

Valine

Leucine

Isoleucine

HO-CH2- Serine

Threonine

Cysteine

Methionine

Aspartic acid

CH3-CH-

OH

CH2-

SH

CH2-CH2-

S-CH3

-OOC-CH2-

Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.6

Protein Digestion and

Absorption


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Protein Digestion

Gastric phase (stomach)

Hydrochloric acid (HCl) from cells in stomach unfolds protein

Pepsinogen (chief cells)HCl

Pepsin (enzyme)

Pepsin digests proteins Large peptide fragments

Small intestine phase

Cholecystokinin (hormone released in upper small intestine)

triggers pancreas to secrete digestive enzymes once digestion

products leave the stomach

Digestive enzymes are activated and continue to break down

peptides into di-/tripeptides and free amino acids, which are

taken up by intestinal cells


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Amino Acid and Peptide Absorption

• Transporters can carry

– Free AAs

– Di- and tripeptides

• For example, can transport carnosine, a dipeptide

– Nonprotein AAs

• For example, can transport creatine from intestine to blood

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Lumen

Amino acids

Oligopeptides TripeptidesDipeptides

Intestinal cell Blood

Cellular membrane

Peptidases

Transporters


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Fast Versus Slow Digestion of Proteins

• Proteins are digested at different rates– Similar to glycemic index concept for carbohydrates

• Whey vs casein– _____ is rapidly digested and results in quick rise in plasma AAs

(fast protein)

– ______ forms a curd and takes longer to empty from the stomach (slow protein)

• Less dramatic, but more sustained rise in plasma AAs after consumption

• Soy protein– Digested faster than whole milk protein, which contains both

whey + casein

• Overall, more like a fast protein, but slower than whey 11


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Protein Turnover

• There is a constant flux between making new muscle

protein and breaking down old muscle protein

– Known as “protein turnover”

• Goal for increasing muscle size is for muscle protein

synthesis to exceed breakdown

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Muscle

synthesis

Muscle

protein

Muscle

breakdown

Amino

acids

Amino acidsBlood


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Fast- vs. Slow-Digested Proteins in

Protein Turnover

• Milk proteins are superior to soy for

stimulating protein synthesis

– Whey (fast protein) stimulates protein synthesis

to a greater extent than casein (slow protein)

and soy (moderate-fast protein)

– Casein reduces muscle protein breakdown better

than whey protein

• Mixed protein sources provide benefits of all

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Branched Chain Amino Acids (BCAAs)

• BCAAs are:

• Unlike other AAs, most BCAA metabolism occurs in

skeletal muscle

– Liver lacks first 2 enzymes in the pathway that break

down BCAAs

• Leucine is also unique among AAs in its ability to

stimulate synthesis of new muscle proteins 15

CH2

H3C

H3C

CH-

H3C

H3C

CH-CH2-

CH2

CH-

CH3

C COO-

NH3+

H

C COO-

NH3+

H

C COO-

NH3+

H

Leucine Isoleucine Valine


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BCAAs and β-hydroxy-β-

methylbutyrate (HMB)

• What is HMB?– Derived from breakdown of leucine

– Hypothesized to inhibit muscle protein breakdown

and increase muscle synthesis, especially in

combination with resistance training

– Some evidence in humans that doses of 3 g/day may

be effective

• Additive benefits with creatine

– Some studies suggest that HMB may provide greater

benefit to untrained people who start weight

training compared with previously conditioned

athletes16


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Protein Quality

• Complete protein

– Contains all the essential AAs in amounts that meet or exceed the amounts needed by humans

• Animal proteins (except gelatin)

• Soy protein

• Incomplete protein

– Too low in one or more of the essential AAs to support human growth and development

• Cannot serve as a sole source of protein in the diet

• Most plant proteins are incomplete proteins (except soy)

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Protein Quality (cont’d)

• Complementary proteins

– Combinations of incomplete proteins that,

when added together, result in a complete

protein

• Legumes: methionine, lysine

• Grains: methionine, lysine

• Example: rice and beans

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Protein Quality (cont’d)

– Usually, combining a complete protein with an incomplete protein is considered complementary• Exception is milk and legumes

– Although milk has a greater amount of sulfur-containing AAs (eg, methionine and cysteine) per gram compared with legumes,

• Not enough sulfur-containing AAs are present for an ideal AA profile when the 2 foods are consumed together

– Combining complementary proteins at each meal for vegetarians is not necessary• What matters is total intake of complementary

proteins spread over the course of the day

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Determining Protein

Recommendations

for Athletes


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Protein Requirements

• Current RDA for protein is 0.8 g/kg body weight per day

• The RDA for protein is set to prevent deficiency (ie, maintain protein balance) in healthy adults

• Does not consider potential benefits that might be obtained from amounts beyond RDA• For example, the optimal protein intake for muscle

function and athletic performance

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Protein Intake

Recommendations

• American College of Sports Medicine (ACSM)

/ American Dietetic Association (ADA)

–Endurance athletes, 1.2 to 1.4 g/kg per day• Accounts for greater use of protein as fuel for energy

–Strength athletes, 1.2 to 1.7 g/kg per day• To support muscle growth, particularly during early training phase when

gains are greatest and protein utilization is less efficient

• Clinical studies suggest there is no apparent

benefit at intakes above 2.0 g/kg per day

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Vegetarian Diets

• Most vegetarian athletes meet the RDA

for protein of 0.8 g/kg per day

• Protein quality of non-animal / non-dairy

sources is lower

• ACSM/ADA recommends 1.3 to 1.8 g/kg

per day for vegetarian athletes

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How Much Protein Are Athletes

Eating?• Many athletes may already meet or exceed

protein recommendations• Definition of “high protein” can be the absolute

amount of protein, % of total energy (calories), or protein ingested per kg of body weight

• Strength athletes in particular may believe that much higher protein intakes are needed for muscle building• Intakes at 4- to 6-g/kg range are not uncommon

• Unlikely to provide benefit beyond 2.0 g/kg

• It is possible that this much protein intake could adversely affect the nutrient quality of the overall diet

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How Much Protein Are Athletes

Eating?

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• Protein intake below 2 g/kg per day is safe

in healthy individuals

• Protein intake above 2 g/kg per day is not

recommended due to lack of proven benefit

and potential for adverse health effects


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Potential Downside to “High-

Protein” Diets

• Hydration status

• Nitrogen that is obtained from consuming protein must be excreted in the urine as urea

• Increased urinary output due to high protein load may increase chances of dehydration

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Protein” Diets

• Diets very high in protein may lack appropriate amounts of carbohydrate, fiber, and some vitamins/minerals

• Could impair exercise performance

• Could increase long-term risk of diseases such as colon cancer

• Possibly due to lack of fiber or increased intake of red meat

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Protein” Diets

• Excessively fatty protein sources could increase risk of cardiovascular disease

Choose mostly lean protein sources

For example, salmon is more desirable than a ribeye steak

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Protein” Diets

• Kidney disease

• No good evidence of damage in individuals with healthy kidneys

• Protein-rich diets are high in phosphorus, which can be harmful to individuals with kidney disease – Primarily a concern with elderly or sick

individuals, as opposed to healthy athletes

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Protein” Diets (cont’d)

• Bone health

• Higher protein diets may increase calcium loss in urine

–However, gut absorption of calcium is likely improved, so there may be no net difference

• Elevated protein diets appear to have either no or a slightly beneficial effect on skeletal health

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Summary of Protein

Recommendations• Daily Recommended Intake is 0.8 g/kg per day

(2002)–No recommendation for increase in athletes

• American College of Sports Medicine– Strength athletes: 1.2 to 1.7 g/kg per day

– Endurance: 1.2 to 1.4 g/kg per day

• Vegetarians may have higher dietary supplementation protein needs than omnivores

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Summary of Protein

Recommendations• Protein intakes up to 2.0 g/kg per day are

generally safe in healthy adults and may be beneficial• Many athletes may already unconsciously eat this

amount of protein

• Few convincing data show that > 2 g/kg per day is helpful• May actually increase risk of adverse events

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What About Amino Acid

Supplements?

• As long as the complete protein requirements are met, the individual AA requirements will be met as well No need for additional AA supplements to prevent

deficiency

• Because vegetarians eat few complete sources of protein, they should be cognizant of complementary protein sources throughout the day to prevent deficiency of particular AAs

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What About Amino Acid

Supplements?

• BCAA are popular as a supplement among athletes – Claims mainly center on decreasing muscle soreness

and improving either performance or recovery from exercise

– Doses can range from 2 to 7 g/day to more than 20 g/day

• There are potential risks associated with AA supplements• Large doses of single AAs can prevent the

absorption of other AAs, which may lead to diarrhea

• Can indirectly cause deficiency of other AAs as a result 34


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Is Protein Used for Energy

in Athletes?

• In general, the body prefers to spare its own

protein stores from use for energy production

• Skeletal muscle, in particular, will be protected in

order to allow crucial fight or flight response

• Only in conditions of starvation or extreme energy

requirements (eg, ultramarathons) will the body

break down muscle for energy

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Is Protein Used for Energy

in Athletes?

• Dietary protein is commonly used as a fuel

source in certain situations (eg, during

endurance exercise, which can deplete

carbohydrate stores in muscle)

• 6 of the 20 amino acids can be metabolized for

energy in resting muscle (frequent during exercise)

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Timing of Ingestion and Macronutrient

Content of Meals

• There is increasing agreement that immediate post-exercise ingestion of protein and/or carbohydrate has beneficial effects on• Muscle glycogen replenishment (particularly

carbohydrate)

• Muscle protein synthesis (particularly protein)

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Timing of Ingestion and

Macronutrient Content of Meals

• A combination of both protein and carbohydrate work better than either carbohydrate or protein alone• Proportions of carbohydrate/protein vary based on

individual needs• Endurance athletes prioritize carbohydrate intake for

glycogen replenishment

• Bodybuilders prioritize protein intake for muscle growth

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Putting a Meal Plan Together

• Example: 70-kg athlete requiring 4,000 kcal/day who is exercising 120 min/day, 4 to 6 times/week

• Macronutrient target recommendations

– Grams/kg body weight/day

• Carbohydrate 7-10 g/kg (490-700 g/day)

• Protein 1.5-2.0 g/kg (105-140 g/day)

• Fat Typically use percentage of energy

– Percentage of energy

• Carbohydrate 55-65% of energy (550-650 g/day)

• Protein 10-15% of energy (100-150 g/day)

• Fat 20-30% of energy (88-133 g/day)

• Target recommendations for this athlete

− Carbohydrate 600 g/day (60% of energy)

− Protein 130 g/day (13% of energy)

− Fat 120 g/day (27% of energy)39


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Remember!

• For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day (g/kg/d)

• higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals (i.e., promote loss of fat mass).

• General recommendations of 0.25 g of a high-quality protein per kg of body weight, or an absolute dose of 20–40 g to maximize MPS.


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Remember!

• Acute protein doses should strive to contain 700–3000 mg of leucine and/or a higher relative leucinecontent, in addition to a balanced array of the essential amino acids (EAAs).

• Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS.

• Different types and quality of protein can affect amino acid bioavailability following protein supplementation.


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Remember!

• Athletes should consider focusing on whole food sources of protein that contain all of the EAAs (i.e., it is the EAAs that are required to stimulate MPS).

• Endurance athletes should focus on achieving adequate carbohydrate intake to promote optimal performance; the addition of protein may help to offset muscle damage and promote recovery.

• Pre-sleep casein protein intake (30–40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis.


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Summary

• Adequate protein intake is critical for athletic

performance and good health

• For most athletes, protein intakes of 1.5 to 1.8

g/kg/day will meet protein requirements

• High-quality protein sources (eg, dairy products,

meats, fish, chicken, soy, eggs) should be included

in the diet

• Eating a combination of carbohydrate and protein

soon after exercise can help with muscle recovery

and muscle building

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Summary

• There are potential disadvantages to excessive

protein intake above 2 g/kg/day

• No additional benefit for strength or muscle

building

• Increased water loss from the body that may lead

to dehydration

• High-protein intake may replace carbohydrates and

other vital nutrients for athletic performance and

good health

• Decreased overall diet quality

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Gracias

protein in exercise

Health & Medicine