Staying on Versus Going Off a Diet: Effects on Eating in Normal Weight -

and Overweight Individuals

Michael R. Lowe

(Accepted 3 December 1991)

Past studies on the behavioral effects of dieting in overweight individuals have produced conflicting results. Overweight restrained eaters and self-initiated dieters have eaten little whether preloaded or not, whereas overweight individuals who have lost weight in weight reduction programs have eaten a lot whether preloaded or not. The present study examined the effects of requiring overweight self-initiated dieters to stay on or "go off" their diets for 2 days. A control group of normal weight self-initiated dieters was subjected to the same di- eting manipulation. All subjects then participated in an ostensible ice cream taste test, Overweight subjects who stayed on their diets ate almost twice as much as overweight sub- jects who went off their diets; the intake of normal weight subjects was unaffected by the dieting manipulation. A cognitive explanation was developed to account for the findings of the present study along with those of past studies on self-initiated and weight-loss dieting. 0 1992 yohn Wiley & Sons, Inc.

There are conflicting findings on the effects of dieting on eating regulation in over- weight individuals. Overweight restrained eaters (Ruderman & Christensen, 1983) and overweight individuals on self-imposed diets (Lowe, Whitlow, & Bellwoar, 1991) eat little in laboratory eating tests whether or not they are preloaded. Overweight dieters who have lost weight in a weight loss program, on the other hand, eat a lot whether or not they are preloaded (Rodin, Moskowitz, & Bray, 1976; Wardle & Beales, 1988).

How might these divergent eating regulation patterns of obese self-initiated dieters (i.e., those who are restraining their eating or dieting on their own) and obese weight- loss dieters be explained? Restraint theory, the prevailing model for understanding the behavioral effects of dieting (Polivy & Herman, 1985), does not appear to be capable of accounting for this pattern of findings. After all, neither of the aforementioned eating patterns conform to the predictions of restraint theory (i.e., neither overweight self- initiated dieters nor overweight weight-loss dieters engage in counterregulatory eat- ing).

Michael Lowe is an Associate Professor in the Division of Clinical Psychology at Hahnemann University. Requests for reprints should be addressed to Michael K. Lowe, Division of Clinical Psychology, Mai l Stop 626, Hahnemann University, Philadelphia, PA 79702.

International journal of k i t ing Disorders, Vol. 12, No. 4, 417-424 (1992) 0 1992 by John Wiley & Sons, Inc. CCC 0276-3478l92lO45417-08

41 8 Lowe

Since obese dieters who actually lost weight in a weight loss program had undoubt- edly lost more weight in the recent past than obese restrained eaters or those on self- imposed diets, it is possible that the existence of a greater negative energy balance among weight-loss dieters could explain their increased vulnerability to overeating. However, while biological reactions may have contributed to the increased eating of weight-loss dieters (cf. Polivy & Herman, 1985), a biological explanation does not ap- pear to be sufficient to explain these results (Lowe, 1987). For instance, Wardle and Beales’ subjects significantly increased their eating even though their reduction in body weight (about 2%) was rather trivial biologically, especially among overweight people with extra fat stores. Also, it appears that people generally are not very responsive to biologically-generated cues associated with short-term caloric deprivation (Rodin, 1981).

Another possible explanation for the divergent eating patterns of self-initiated diet- ers (Lowe et al., 1991; Ruderman & Christensen, 1983) and weight-loss dieters (Rodin et al., 1976; Wardle & Beales, 1988) is that these groups differ in regard to the “cogni- tive set” they adopt toward their diets. Eating restrictions practiced by self-initiated di- eters are self-imposed, whereas eating restrictions practiced by weight-loss dieters are externally imposed. Thus people on self-initiated diets may have more internally- generated motivation to adhere to their dietary guidelines when temptation arises. In- dividuals who join a weight loss program, on the other hand, may relinquish control of their eating to external sources, increasing the probability that they will ”look out- ward” for guidance concerning their eating. Thus when weight-loss dieters (Rodin et al., 1976; Wardle & Beales, 1988) are encouraged to eat all they want of a “fattening” food- in the same setting where they have been taught to eat less food- they may feel quite justified in “letting go” and splurging. This viewpoint could explain why self- initiated and weight-loss dieting have had different effects on eating in past studies. It could also explain why obese subjects’ post-weight loss increase in eating occurs inde- pendently of preload status and why these subjects eat more after dieting whether the diet produces large (Rodin et al., 1976) or small (Wardle & Beales, 1988) weight losses.

The main purpose of the present study was to test this cognitive explanation for the aforementioned differences in eating behavior between self-initiated dieters and weight-loss dieters. This was done by selecting a group of overweight self-initiated di- eters and requiring half of them to stay on their diets and half of them to “go off” their diets. The duration of this diet manipulation was intentionally kept brief (2 days) so that the energy balance differential between the two groups would be negligible. At the end of this diet manipulation phase, subjects participated in a standard ice cream ”taste test” in a nonpreloaded state. This methodology was designed to mimic the re- quired dietary restrictions imposed by weight loss programs (Rodin et al., 1976; Wardle & Beales, 1988), among self-initiated dieters who have previously been found invulnera- ble to overeating (Lowe et al., 1991). If the external imposition of a dietary regimen increases susceptibility to overeating in overweight individuals, then self-initiated diet- ers who are required to stay on their diets should eat more in the eating test than self- initiated dieters who are required to go off their diets.

Since past evidence of increased eating following weight loss was gathered primarily among overweight individuals (Rodin et al., 1976; Wardle & Beales, 1988), it is un- known whether such eating changes would occur equally among normal weight indi- viduals. Thus a comparison group of normal weight self-initiated dieters was included in the design so we could determine the extent to which the effects of the short-term dieting manipulation are associated with obesity per se.

Dieting and Eating

METHOD

41 9

Subjects

Subjects were 40 undergraduate female students drawn from both Rutgers and Tem- ple Universities. Eligible subjects were identified through a "Weight History Question- naire" administered in psychology classes. Normal weight and overweight students who indicated that they were "currently on a diet to lose weight" (Lowe et al., 1991) were selected for participation.

The final subject sample consisted of 20 normal weight ( 4 5 % over the midpoint for desirable weight for height on the Fogarty tables) and 20 overweight (215% over desir- able weight) dieters. Weight classification was based on height and weight measured in the laboratory. Data for three overweight dieters were discarded because of their failure to adhere to experimental procedures.

Procedure

Eligible respondents were called and told that we were conducting a study on the "relationship between short-term dieting and taste preferences." They were asked if they were currently dieting to confirm that their designation as "dieters" was still accu- rate. Two students who said they were no longer dieting were excluded from the study.

The students were told that some dieters, chosen at random, would be asked to re- main on their diets for 2 days prior to engaging in a taste preference test, and that other dieters would be asked to "go off" their diets for 2 days by increasing their nor- mal caloric intake by one-third or 500 calories, whichever was larger. The subject was told that this was being done to investigate the effect of short-term dieting on taste preferences. The subject was also informed that she had to decide whether to partici- pate in the study without knowing the condition to which she would be assigned. Three students were not willing to comply with this requirement and did not partici- pate.

The subject was then told that we needed to get an idea of her typical caloric intake in order to assign her to the appropriate level of caloric intake during the 2-day study period. The subject was asked to list everything she had eaten and drunk that day, as well as anything she intended to eat before bedtime. The research assistant then sched- uled each subject for two appointments, to be held 2 days apart.

A research assistant calculated subjects' caloric intake using a standard calorie-count- ing book and then randomly assigned each subject to either continue dieting or stop dieting for 2 days. Estimated caloric intake was rounded off to the nearest 50-calorie increment. The caloric goal for subjects assigned to continue dieting was this rounded- off estimate of their caloric intake while dieting. The caloric goal for subjects assigned to "go off" their diets was one-third or 500 calories higher than their estimated intake, whichever was greater.

The night before her first appointment, each "ongoing-diet" subject was informed of her experimental assignment and was told that she should simply continue dieting as she had been. She was given her estimated caloric intake as her caloric goal for the 2-day monitoring period. She was also told about possible reactive effects of self- monitoring and advised to resist any reluctance she might feel to eat some foods she normally would. The "interrupted-diet" subjects were given their caloric goals, advised

420 Lowe

about possible self-monitoring reactivity, and asked to make sure they ate enough to reach their (elevated) caloric goals.

Subjects came to their first appointment the next morning. They received two food monitoring forms and detailed instructions about recording all food intake, even if their intake deviated from the instructions they were given for caloric intake. Subjects were told to describe their intake in detail, including brand names (e.g., McDonald’s french fries), portion sizes, ingredients, and methods of preparation (deep frying, broiling, etc.).

Subjects were called the night before their second session. They were told to eat whatever breakfast was appropriate for their condition and to have nothing to eat be- tween then and their appointment at our lab. The second session was held between 11:OO AM and 1:30 I’M. Subjects were run by one of three female research assistants who were blind to subjects’ dieting condition.

At the second session, subjects were seated in a small (8’ X 10’) room furnished with a table, table cloth, and chair. They were given a simple 10-point hunger rating scale (1 = extremely hungry, 10 = extremely full) to complete before the beginning of the ”taste perception test.” The experimenter then left and returned with three bowls con- taining 500 grams of chocolate, vanilla, and strawberry ice cream, a spoon, napkin, and three “taste rating” sheets. Instructions for the “taste perception test” were similar to those used by Herman and Mack (1975). Subjects were asked to taste and rate each flavor of ice cream, and were encouraged to help themselves to any remaining ice cream when they finished their taste ratings.

At the end of the 10-minute eating test, the experimenter reentered the room, col- lected the ice cream, and reweighed it in another room. The subject then had her height and weight measured on a balance beam scale (without shoes), was debriefed, and was paid for her participation.

RESULTS

Preliminary Analyses

The mean percentage overweight for the normal weight subjects was 1.5 (range = -10.0 - 14.3) and for the overweight subjects was 41.3 (range = 15.8-82.3; see Table

Several measures of subjects’ caloric intake are shown in Table 1. Subjects’ mean es- timated daily caloric intake (from the telephone interview) was 1,198, suggesting that these subjects were indeed on hypocaloric diets. Overweight dieters’ estimated intake was marginally higher than normal weight dieters’, F(1, 36) = 3.4, p = .07.

As shown in Table 1, the mean assigned level of daily caloric intake for subjects who stayed on their diets was about the same as their estimated caloric intake, whereas the mean assigned level of intake for subjects who went off their diets was an average of about 500 calories higher than their estimated intakes. The “average intake” row re- flects the mean of the 2 days of self-monitored caloric intake. Subjects who stayed on their diets consumed approximately 700 caloriedday less than subjects who went off their diets, F(1,36) = 25.4, p < .001. The degree to which subjects’ actual caloric intake approximated their assigned intake level is shown in the next row, “% discrepancy in intake.” This measure was derived by finding the difference between subjects’ average intake and their assigned intake, and dividing the difference by their assigned intake.

1).

Dieting and Eating 421

Table 1. and weight status

Eating and weight-related characteristics of subjects by dieting condition

Dieting Condition

Stay On Diet Go Off Diet

Normal Weight Overweight Normal Weight Overweight

Measures M SD M SD M SD M SD

% Overweight 3.3 6.7 41.8 20.4 -.2 7.3 40.7 22.4 Estimated 1,107 214 1,286 417 1,101 252 1,299 361

Assigned 1,109 209 1,285 416 1,606 244 1,835 403

Average 1,189 515 1,299 433 2,104 461 1,853 429

% 5.4 31.6 2.9 22.0 33.1 36.7 2.7 19.7

intake

intake

intake

Discrepancy in intake

ratings Hunger 4.4 1.4 4.0 .9 5.3 1.3 5.0 1.0

Grams eaten 114.0 68.8 163.4 69.0 116.9 52.6 83.9 62.5 ~~

Note: N = 10 per cell.

It can be seen that the actual intake of three of the four groups was close to their assigned intake level. However, normal weight subjects who went off their diets “over- shot” their assigned level of caloric intake by 33.1%, far more than the other three groups (2.7-5.4%). A 2 (dieting status) X 2 (weight level) ANOVA conducted on the discrepancy scores (mean intake/day - assigned intake) produced a main effect for weight group, F(1, 36) = 4.93, p < .05, as well as a marginally significant interaction, F(1, 36) = 2.84, p = . lo. While normal weight subjects exceeded their assigned caloric goals more than overweight subjects did, this was primarily due to the excessive con- sumption of normal weight dieters who went off their diets.

Hunger and Eating Data

The means for the hunger ratings and grams of ice cream consumed are shown in Table 1. An ANOVA on the hunger ratings produced a significant main effect for diet- ing condition, F(1, 36) = 5.96, p < .05, with dieters staying on their diets reporting greater hunger than dieters going off their diets. No other effects were significant.

The ANOVA for grams consumed resulted in a marginally significant main effect for dieting condition, F(1, 36) = 3.63, p = .07, qualified by a significant interaction be- tween dieting condition and weight status, F (1,36) = 4.20, p < .05. This interaction is illustrated in Figure 1. While normal weight subjects’ consumption was unaffected by the dieting manipulation, overweight subjects’ eating was strongly affected. Simple ef- fects tests (using the pooled error term) indicated that obese subjects who stayed on their diets ate more than obese subjects who went off their diets, t(18) = 2.79, p < .05, and tended to eat more than normal weight subjects who stayed on their diets, t(18) = 1.74, p < .lo.

As reported above, there was a tendency for normal weight subjects who went off their diets to substantially overshoot their assigned caloric goals. To see if this affected

422 Lowe

170 T

I 150 t

M e

n

G

a

120 +

110-

S

I

70

1 - Normal Wgt. Dieters -t-- Overweight Dieters L

I--- I

Stay On Diet Go Off Diet

Figure 1. Effect of weight level and dieting status on grams of ice cream eaten.

the eating results, the "% discrepancy in intake" score was entered as a covariate in an ANCOVA for ice cream consumed. The intake discrepancy score did not account for a significant amount of variance in ice cream consumption, p > .25, and did not alter the significant interaction found for ice cream eaten.

DISCUSSION

The present results indicated that obese dieters who were required to stay on their diets for 2 days ate almost twice as much ice cream in the eating test as obese dieters who were required to "go off" their diets for 2 days. This eating pattern was unique to obese dieters, since normal weight dieters' intake was unaffected by the same dieting manipulation.

The present findings are consistent with other studies which have shown that diet- induced weight loss among obese individuals produces compensatory appetitive reac- tions which favor restoration of lost weight (Kleifield & Lowe, 1991; Rodin et al., 1976; Wardle & Beales, 1988). The significance of the present findings lies in the possibility that obese individuals' eating is highly sensitive to their dieting status per se. That is, while the eating results from past studies could be explained by reference to weight loss-induced increases in appetite, the present results cannot be similarly explained. The energy intake differential produced by our dieting manipulation- about 1,500 cal- ories over 2 days-was quite small. It would therefore be difficult to explain these re- sults in terms of a weight-sensitive biological regulator (set point, ponderstat, etc.) which was activated to counter the energy deficit created.

Dieting and Eating 423

Since all subjects in this study had already been dieting when they entered the study, the possibility exists that the increased eating of obese subjects who stayed on their diets was due to a more substantial reduction in weight that they were undergo- ing. However, the aforementioned results of Lowe et al. (1991) render this possibility unlikely. Lowe et al. assessed (but did not manipulate) dieting status, and defined di- eting using the same question used in the present study. They found, in the no pre- load condition, that overweight self-initiated dieters ate significantly less than overweight nondieters. If weight loss among self-initiated overweight dieters produces overeating, then overweight dieters in Lowe et al.’s study should have eaten more, rather than less, than overweight nondieters.

It therefore appears that cognitive aspects of the current dieting manipulation may account for its effects in the overweight subjects. However, since the present study did not assess possible cognitive mediators of the observed findings, we can only offer a speculative account of the cognitive processes that may have been involved.

As suggested in the introduction, overweight dieters who were assigned to continue on their diets at a specified caloric level may have relinquished control of their eating behavior to the experimenter. That is, whereas this group had previously been dieting “for themselves,” after their experimental assignment they may have come to view themselves as dieting “for the experimenter.” This could have both undermined their internal motivation to control their eating when the dieting manipulation was over (i.e., during the eating test) and made them more susceptible to the experimenters’ en- couragement to eat freely during the eating test. Overweight subjects assigned to go off their diets, on the other hand, may have retained their internal dieting motivation and tried to ”get back on track as soon as possible (again, at the end of the study when the eating test was administered). These reactions could account for why over- weight subjects who stayed on their diets ate more in the eating test than overweight subjects who went off their diets. This cognitive viewpoint could also be applied to ex- plain why overweight self-initiated dieters ate little regardless of preload status in Lowe et al.’s (1991) study (i.e., because they were internally motivated to stay on their diet) and why weight-loss dieters ate a lot regardless of preload status in the Rodin et al. and Wardle and Beales studies (i.e., because they had relinquished control of their eating to others).

The present results raise several issues which should be investigated in future research. First, the cognitive explanation advanced to account for the results is specu- lative and must be tested directly, e.g., by examining the kinds of attributions self- initiated and weight loss dieters make for their dieting behavior, and by seeing if the manipulation of such attributions alters susceptibility to overeating. Second, future re- search should examine why the eating of obese dieters, but not that of normal weight dieters, was influenced by the present dieting manipulation. Past research has also found differences in the eating behavior of obese and normal weight dieters (Lowe et al., 1991; Ruderman & Christensen, 1983), but little is known about why weight status moderates the effects of dieting on eating. Third, while the present findings for obese subjects who stayed on their diets are in line with prior research (Rodin et al., 1976; Wardle & Beales, 1988), it is important to point out that our approach to studying the effects of dieting differed in an important respect from past studies. We examined the effects of having dieters stay on versus go off a preexisting diet; past studies have exam- ined the effect of instituting a diet in subjects who were not yet dieting. Thus an im- portant task for future research is to determine if the effects of dieting documented here also occur when obese nondieters are put on short-term calorie-restricted diets.

424 Lowe

This study was supported by grant 1 R15 DK38864-01 from the National Institute of Diabetes and Digestive and Kidney Diseases. I wish to thank Bettina Lowe, Melissa Lim, Pamela Mead- owcroft, and Christy Michaels for their conscientious assistance in running this study, and Bill Whitlow for intellectual stimulation and practical support.

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