Physical Activity and LongTerm Maintenance of ... - Wiley Online Library

REVIEW ARTICLE

Physical Activity and Maintenance of Weight Loss

Long-Term

Nicolaas I? Pronk, Rena R. Wing

Abstract To examine the effect of exercise on the long-term maintenance of weight loss, two types of literature were reviewed correlational studies of predictors of long-term weight loss, and randomized trials comparing diet, exercise, and the combination of diet plus exercise. Both literatures were striking in the consistency with which activity emerged as a determinant of long-term maintenance of weight loss. The benefits of exercise for long-term weight maintenance were observed with different types of populations, diets, and exercise interventions. Several possible explanations for these positive effects of diet plus exercise are presented, and suggestions made for future research on ways to maximize the benefit of this approach to weight control. Since adherence to exercise may ultimately prove to be the cornerstone for long-term weight maintenance, studying ways to improve exercise adherence is recommended.

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Key words: exercise, body weight, weight loss and maintenance, obesity, dietary restriction, (OBESITY RESEARCH 1994;2:587-599) Introduction

Obesity is a major health problem in the United States. Over 34 million Americans are obese and the prevalence of obesity is increasing (62). These data argue for increased efforts to prevent obesity and to develop effective treatments for those who m obese. Current treatments for obesity are only moderately successful. Weight loss during the active phase of treatment averages about 10-20 kg; approximately 4040% of this weight loss is regained within one year and a Submittedfor publication June 2.1994. Accepted for publication in final form August 6,1994. From University of Pittsburgh School of Medicine, Westem PsychiatricInstitute and Clinic, 3811 O'Hara Street, Pittsburgh, PA 15213. Reprint requests to Dr. Pronk, University of Pittsburgh School of Medicine, Westan Psychiatric Institute and Clinic. 381 1 O'Hara Street. Pittsburgh, PA 15213. Copyright 81994 NAASO.

complete return to initial body weight tends to occur within five years (45). Numerous correlational studies have been conducted to try to identify predictors of success in long-term weight loss and maintenance. Consistently, these studies point to the adoption of an exercise habit as a key component in successful long-term weight control. Randomized trials comparing diet, exercise, and the combination of diet plus exercise also lead to the same conclusion--tbat the best long-term outcomes occur in treatments that combine diet plus exercise. The purpok of this paper is to review the evidence from correlational studies and randomized trials on the effeci of exercise on the long-term maintenance of weight loss. The effects on this relationship of the type of diet, the type of exercise prescribed, and the population studied will also be examined. Potential mechanisms for the long-term benefits of diet plus exercise will be discussed and suggestions made for future research to maximize the benefits of this approach to weight control. correlational studies Evidence supporting the benefit of exercise for the long-tenn maintenance of weight loss comes first from correlational studies examining the variables associated with successful weight control. Typically, these studies assess the relationship between self-reported physical activity level and weight loss one year after participation in a weight loss program. Before presenting the findings from these studies, it is important to understand the research paradigm that is typically used and the limitations of these studies. In most of these studies, participants are initially tteated in a program which involves multiple intervention strategies, such as cognitive restructuring, selfmonitoring, and modification of eating behavior. These subjects are then re-examined approximately one year after the program. There is usually little contact with the subjects over this year of follow-up, and no direct OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 587

Exercise and Weight Loss Maintenance, Pronk et al.

control is exerted over diet and exercise behavior. Subjects typically self-report their diet, exercise, and use of behavior modification strategies at the follow-up time point, and regression analyses are used to determine which of these variables has the strongest association with long-term weight control. As noted above, the eating and exercise behaviors, and sometimes the weight data, are determined by self-report. Moreover. only a portion of the subjects who participated in the initial program are willing to attend the follow-up; subjects who remain in the study tend to be those who have been most successful. These correlational studies consistently show that self-reported level of exercise is the single strongest predictor of weight loss maintenance. This appears to be the case regardless of whether the population studied involves men (16,29,33,34,42), women (16,28,29,33,34, 36). massively obese individuals (35), adolescents (15), or children (15). Moreover, the association between exercise and long-term weight loss has been observed in studies using moderate dietary restriction (33, 34) or VLCDs (31) during the initial treatment. A recent example of such a study is the one conducted by Kayman and associates (36). These researchers attempted to identify factors that differentiated weight maintainers (n=30) from weight regainers ( n 4 ) and controls (n=34). Maintainers were defined-' as women who had successfully maintained their weight loss for at least two years. Regainers were women who had previously lost 20% of their weight but had regained it. The control women had always been average weight. One of the major differences between the three groups was their exercise behavior. Seventy-six percent of maintainers reported that they used exercise as part of their weight loss strategy compared to only 36% of regainers. Even more striking were the differences in the reported use of exercise as a weight maintenance strategy. Ninety percent of maintainers and 82% of the controls reported engaging in regular exercise (2 3 d/wk for 2 30 min), whereas only 34% of regainers reported this level of activity. Moreover, those regainers who did report regular exercise, exercised less frequently and less vigorously than the maintainers. Similarly, Colvin and Olson (16) found that adoption of a long-term exercise habit was a distinguishing feature of successful weight maintenance. In interviews with 41 women and 13 men who had lost at least 20% of their body weight and maintained that loss for approximately six years, these investigators found that 85% of men and 78% of women reported increased exercise. Interestingly, a greater proportion of men (85%) compared to women (24%) reported that the exercise was vigorous. Other aspects of the initial matment program, including self-monitoring techniques and 588 OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994

increased nutrition knowledge, were also related to weight loss maintenance. Other researchers have presented similar results when subjects were followed for seven months (28), one year (33,34,42) or five years (29). Although few studies have investigated the effect of exercise behavior on long-term weight control in children and adolescents, available data suggest that exercise is also related to long-term weight maintenance in these individuals. Cohen and associates (15) studied 42 children (mean age 13.6 years) who were classified as maintainers, regainers, or normal weight controls. Both regainers and maintainers had attended a children's weight loss program 1-3 years prior to this study, and had lost weight during treatment (15.6% and 9.7% of body weight, respectively). The groups were comparable in elapsed time between treatment and follow-up. The maintainers further decreased their weight by 13.3%over the 1-3 year follow-upinterval while regainers increased their weight by 14.5%. Data obtained from diet and exercise diaries and weight control questionnaires showed that maintainers reported significantly higher levels of physical activity than regainers or normal weight peers. while most of the retrospective studies showing the benefit of exercise for long-term weight maintenance have invohed balanced diets with moderate caloric deficits, studies with very-low-calorie diets (VLCDs) confirm these findings. For example, Hartman and associates (31) evaluated 80 obese subjects 2 to 3 years after treatment in a combined behavior therapy and VLCD program. Exercise participation and enrollment in a weight loss maintenance program emerged as the two correlates of weight loss maintenance. The degree of exercise participation, expressed as weekly energy expended (kdwk), correlated with weight loss at follow-up (r = 0.40). Furthermore, those who reported expending 21OOO k d w k in exercise at follow-up maintained a significantly greater proportion of weight loss than those who expended 0-1OOO k d w k or those who did not ex& at all (67.9%, 42%,and 22.5%,respectively). Similarly, Miller and Sims (43) reported long-term weight loss maintenance results following VLCD (700 kcal/d) treatment. These researchers noted a 7.8 kg weight loss at the end of a four-week in-house treatment program in 62 obese individuals. Following the initial four-week program, subjects returned home and were placed on an 800 kcal/d diet until they reached goal weight. All subjects were taught behavior modification techniques, provided with nurritional information, and given information pertaining to physical activity and the reduction of cardiovascular risk factors. At the one-year follow-up, mean weight loss had increased to 13.2 kg. When successful subjects (those who lost more than

Exercise and Weight Loss Maintenance, Pronk el al.

15.9 kg of body weight) were compared to unsuccessful subjects (those who lost less than 9.0 kg of body weight), exercise, in addition to cognitive restructuring, eating style, and social skills, was related to success. These correlational, cross-sectional studies are striking in their consistency. Regardless of the population studied or the type of diet utilized, exercise emerges as a significant predictor of long-term weight loss. However, as noted above, these retrospective data should be interpreted with caution. These results are based on self-report data for the level of exercise, and subjects may not accurately report their exercise level (41). Moreover, distortions in self-reported exercise level may be related to the degree of success at weight maintenance - i.e., those subjects who have kept off their weight may believe that they have become more active, whereas subjects who know they have regained their weight may look for explanations of their poor outcome. These individuals may be biased toward reporting lower levels of activity to “explain” their weight regain. Secondly, changes in physical activity may serve as a marker for other behavior changes. Individuals who are increasing their physical activity may also be modifying the quality and/or quantity of food they consume. It is hard to determine whether it is the exercise per se or this constellation of behavior changes that produces the favorable long-term results. Finally, since these data are Correlational in nature, no cause-and-effect relationship may be inferred. Rather than exercise producing long-term weight loss, it may be that subjects who are successful at weight loss feel good about themselves, and hence are more likely to adopt and maintain an exercise regimen.

studies concern body weight, which is usually obtained by weighing subjects directly. Again, not all subjects are willing to attend the follow-up and the less successful subjects tend to be the ones who are lost to followup. Analyses at the end of matment and at follow-up are done comparing the weight loss of the subjects who were initially assigned to diet, exercise, or the combination group. There is often very little information presented to determine, for example, whether subjects in the exercise only group continued to exercise or whether they also changed their diet over time. Nevertheless, the results of these studies are again persuasive in their consistency. Subjects randomized to the diet plus exercise conditions consistently have better long-term weight loss than the subjects treated with diet alone. The benefit of combining diet plus exercise, vs. diet only, on the long-term maintenance of weight loss has been observed across a variety of populations (26,63,65), and seems to occur regardless of the type of diet (46, 57) or exercise (26) used. Far fewer studies have compared diet plus exercise versus exercise alone conditions (19, 32), but here too, subjects treated initially with diet plus exercise appear to maintain their weight losses better than those treated with exercise only. A summary of randomized controlled trials including at least 6 months of follow-up, is presented in Table 1.

Early Treatment Studies The earliest randomized studies evaluating the role of exercise on long-term weight maintenance included investigations by Harris and Hallbauer (30), Stalonas et al. (59), and Dahlkoetter et al. (19). Harris and Hallbauer (30) compared the effects of a behavioral treatment program for overweight adults that was aimed either at changing eating habits or changing both eating Randomized Controlled Trials Stronger evidence for the importance of physical and exercise. While both groups received the same activity in the long-term maintenance of weight loss information regarding diet, only the latter group was comes from randomized, controlled trials comparing given information about exercise behavior and encourdiet-only, exercise-only, and the combination of diet- aged to implement a self-directed exercise program. plus-exercise. Again, before addressing the results of Following 12 weeks of treatment, the diet-only group these studies, it is important to consider the study design had lost 3.1 kg and the diet-plus-exercisegroup had lost that is used. In these studies, subjects are randomly 4.1 kg. At 7-month follow-up both groups had assigned to one of several treatment groups (diet only, increased their weight loss, but the diet-plus-exercise exercise only, or the combination) and are instructed to group maintained an overall weight loss of 5.9 kg vs. change only the targeted behavior. Therapist contact is 3.9 kg in the diet-only group. Similar results were obtained by Stalonas, Johnson, usually comparable across conditions, but one group is taught to change their eating behavior (plus instructed and Christ (59). These investigators recruited 48 overnot to change their exercise) while another group is weight adults and randomly assigned them to four instructed to change their exercise without modifying groups. All groups received a basic weight loss protheir diet. Following the treatment program, subjects gram consisting of 10 weekly behavioral therapy sesare seen much less frequently (or not at all) and then re- sions. Group 1 received the basic program only, but in examined at 6, 12, or more months following the treat- groups 2, 3, and 4 the basic program was supplemented ment. The primary data collected at follow-up in such with either a non-supervised exercise program, a selfOBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 589

Exercise and Weight Loss Maintenance, Pronk et at.

Table 1. Summary Table of Randomized Controlled Trials Evaluating the Role of Exercise on Long-Term Weight Maintenance ___________Co-en& ___________ Croup CharacteristicdTypeof Diet

-Treatment Weight Loss Qg)------Overall Weight Loss Qg)---Duration Duration (wk) D E D+E (mo) D E D+E

References

Dahlkoetter et al. (19)

8

6

3.2 2.8

(30) Hartwell et al. (32)

7

3.1 4.1

10

6

2.5 0.7 0.2

King et al. (37)

12

Pavlou et al. (46)

8

7.1 9.6 10.6 13.2

18

12.0 12.1 12.5 12.3

Perri et al. (47)

20

18

7.9 8.6 10.3 10.9

Perri et al. (48)

20

Sikand et al. (57) Stalonas et al. (59)

17

Wing et al. Study1 (63)

18

10.8 13.7 11.3 13.1 13.7 17.5

24 21.8

10

4.7 4.5

12 5.9 4.3 7.3 8.5

10

5.6

Study 2

BT BCDD BT, NSE BCDD 7.3 BT, NSE 3.9 BT BCDD BCDD 5.9 BT; NSE 3.5 BT BCDD BT; SE 1.4 BCDD 0.2 BT, SE 3.2regain Maintenance Intervention Assessment Only Condition 2.6 regain Maintenance Intervention; NSE 0.8 regain 3.9 regain Assessment Only Condition; NSE BCDD 13.5 r3.5 PSMF (loo0 kcal/d) r1.2 VLCD (800 k c a d ) 11.0 VLCD (420 kcal/d) BCDD = 9.2 SE PSMF (loo0 kcal/d) 112.3 SE = 8.5 SE VLCD (800 kcalld) = 9.5 SE VLCD (420 kcalld) 0.9 BT BCDD BT, MMP BCDD 5.1 3.1- BT, NSE BCDD BCDD 7.6 BT, NSE; MMP 3.6 BT BCDD BT, Contact BCDD 11.4 8.4 BT, Contact; Social Influence BCDD BCDD 9.1 BT; Social Influence; SE 13.5 BT; Contact; Social Influence; SE BCDD 0.8 BT VLCD VLCD 9.1 BT; SE 2.4 BT BCDD 5.2 BT; Contingency Component BCDD 7.4 BT, NSE BCDD 5.9 BT, Contingency Component; NSE BCDD BCDD 4.0 BT, Placebo SE (Calisthenics) 7.8 BT, SE BCDD 2.8

6.0

Harris & Hallbauer 12

2.3

12

12

3.8 7.9

9.3

Wood et al. (64) Wood et al. Men (65) Women

52

7.2

52

5.1

4.0

BT BT; SE

BCDD BCDD BCDD

SE 8.7

SE

BCDD BCDD

5.1

SE

BCDD BCDD

4.1

Note: BCDD = Balanced Calorie Deficit Diet; BT = Behavioral Treatment; D = Diet-Only Group; D+E = Diet plus Exercise Combination Group; E = Exercise-Only Croup; MMP = Multi-Component Maintenance Program; NSE = Non-Supervised Exercise; PSMF = Protein Sparing Modified Fast; SE = Supervised Exercise; VLCD = Very-Low-CalorieDiet. ~

590 OBESITY RESEARCH Vol. 2

No. 6 Nov. 1994


reinforcement manipulation, or the combination of exercise and self-reinforcement. No differences in weight losses were observed at the end of the 10-week program (mean weight loss 4.8 kg). but at 1-year follow-up, the weight losses of groups 1-4 were 2.4, 7.4, 5.2, and 5.9, respectively. Although no direct comparison was made between groups 1 and 2, a tendency toward a main effect for exercise at one year (p < .lo) was noted. Building on these studies, Dahlkoetter and associates (19) compared the effects of dietonly, exercise-only, and diet-plus-exercise. The dietonly group received an %week behavior therapy program in which food intake patterns were modified. Subjects in the exercise-only treatment self-monitored their activity patterns, made exercise a regular part of the daily routine, and were introduced to social support and reinforcement strategies for physical activity. The diet-plus-exercise group combined these two intervention strategies. At the end of the 8-week program, the diet-plus-exercise group had lost significantly more weight (6.0 kg) than the diet-only (3.2 kg) or the exercise-only (2.8 kg) groups. Moreover, at 6-month follow-up, the combination group again had the best weight loss (7.3 kg in combination vs. 2.8 kg group in exercise only and 2.1 kg in diet only). Thus, all three of these early randomized trials (19, 30, 59) suggested that the addition of exercise to dietary treatment might slightly enhance initial weight loss, but appeared to exert its major effect in the maintenance ofweight loss. This may well result from the fact that the number of calories used in exercise is relatively modest; with continued participation in exercise, these caloric expenditures add up and result over time in more significant weight loss. Recent studies support this contention, and extend the finding to various dietary regimens and patient populations. More Recent Treatment Studies Recent behavioral treatment programs have included longer periods of initial intervention (e.g., weekly meetings for 20-24 weeks), longer follow-up intervals, and greater supervision of the exercise intervention. For example Perri et al. (47) randomly assigned two groups of subjects to receive a behavior therapy program focusing on diet only while two other groups focused on diet plus exercise. The exercise consisted of walking and stationary cycling, 20 minutes per day, 4 days per week, for a target level of 800 kcal per week. Subjects participated in one supervised exercise session each week, held during the weekly behavior therapy meeting, and then completed the other exercise sessions on their own. At the end of the 20-week program, weight loss of subjects in the diet-only groups averaged approximately 8.3 kg compared to 10.7 kg in the diet-plus-exercisecondi-

tions (data provided by Dr.M. Perri, personal communication, 1994). During the 18-month follow-up, the two treatment conditions were crossed with two post-treatment conditions, i.e., no post-treatment contact or a multicomponent maintenance program. The multicomponentmaintenance program consisted of enhanced support and advice and included self-monitoring, peer support, mailings and telephone contact, and was associated with improved maintenance of weight loss, in both the diet only and diet plus exercise condition. At l8-month follow-up, the best overall weight losses were for those subjects who were initially treated with diet-plus-exercise and then later given the multicomponent maintenance program (7.6 kg vs. 0.9 - 5.1 kg for the other three conditions). The only studies which have provided supervised exercise for a full year and evaluated the effects of diet only, exercise only and the combination of diet plus exercise are those by Wood and colleagues (64,65). These investigatorsfirst studied 131 men who were randomly assigned to a control, diet-only or exercise-only group (64).Subjects in the diet program had significantly greater weight loss and loss of lean body mass than the exercise alone group, with no differences in loss of fat mass. The diet group reduced total body weight by 7.2 kg ?f which 1.3 kg was lean body mass and 5.9 kg was fat mass. In contrast, the exercisers lost a total body mass of 4.Qkg but gained 0.1 kg of lean tissue, thereby reducing total fat mass by 4.1 kg. Although this original report did not include a longterm follow-up, the subjects in this study were subsequently enrolled in a maintenance study conducted by King and associates (37). Now, dieters (n=36) and exercisers (n=36) were randomly assigned to either a maintenance program or an assessment-only control condition. The maintenance program consisted of monthly mailed information packets and monthly to quarterly telephone contacts. At the end of the l-year maintenance program, dieters were noted to have regained 3.2 kg (42.1%) and their assessment-only counterparts regained 2.6 kg (40.6%). Interestingly, the exercise maintenance group only regained 0.8 kg (17.4% of their initial weight loss), a significantly lower weight regain than their assessment-only control group who regained 3.9 kg (70.9%). These data indicate that exerciseinduced weight loss may be maintained more easily than diet-induced weight loss by use of a simple, inexpensive maintenance pgram involving mailing and phone contacts. In their next study, Wood and associates (65) compared a diet-only condition with the combination of diet plus exercise; this time both men (n=132) and women (n=132) were studied. The diet program was based on the National Cholesterol Education Program Step 1 diet. OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 591


Exercise was aerobic in nature (brisk walking and jogging) and was supervised three days per week. Both men and women in the diet-plus-exercisecondition had significant increases in maximal aerobic capacity, as assessed by graded maximal treadmill test with measured oxygen uptake. At one year, the men in the dietplusexercise group had significantly greater weight loss than those in the diet-only group (8.7 kg vs. 5.1 kg, respectively) whereas for women, the difference in weight loss between these two groups was not significant (5.1 kg vs. 4.1 kg for diet-plus-exercise and dietonly group, respectively). This study was the first randomized trial to examine the effects of diet plus exercise separately in men and women. The finding that the effects of adding exercise to a dietary treatment program may be greater in men than in women is provocative and should be replicated. It may be that the men in the Wood study exercised more vigorously or frequently than the women, thereby increasing the caloric deficit induced by the physical activity. This contention is supported by the larger as increase in aerobic capacity in men (8.6 &g/min) compared to women (6.4 mlAcg/min) and the longer distance walked or run per week by the men (14.7 km) compared to the women (12.5 km). In future studies it would be interesting to examine this gender difference further and to determine fxst whether the combination of diet and exercise is indeed particularly helpful in the treatment of overweight men and second whether this is due to differences in the level of exercise achieved or in the physiological response to exercise. Studies with Non-Znsulin-Dependent Diabetic Patients Another direction taken in recent studies of diet plus exercise has been to determine whether the combination of diet plus exercise is particularly useful in the management of obese patients with non-insulindependent diabetes mellitus (NIDDM). Since exercise has independent effects on insulin sensitivity (21,54) and glycemic control (55). the combination of diet plus exercise has been hypothesized to be particularly helpful for this patient group. Wing and associates (63) conducted two randomized trials of the combination of diet plus exercise in the treatment of obese NIDDMs. First, a diet-plus-exercise treatment was compared to a dietplus-placebo exercise condition. The placebo exercise program was developed to control for the non-specific aspects of participating in an exercise program. Both groups participated in supervised exercise twice per week; subjects in the exercise group used this time to walk a 3-mile route, while those in the placebo exercise group participated in very-low-intensity exercises and stretching routines. Both groups were instructed to exercise once a week on their own. No significant dif592 OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994

ferences between the moderate and placebo exercise groups were noted for weight loss following 10 weeks of treatment (8.5 vs. 7.3 kg, respectively) or at 1-year follow-up (4.0 vs. 7.8 kg, respectively). In a second investigation, more extreme conditions were compared in order to maximize group differences. Now, one group received a diet-only treatment while the diet-plus-exercise group participated in a supervised 3mile walk three times per week and added an additional walk on a fourth day on their own. Significantly grater weight loss was observed for the diet-plus-exercise group compared to the d i e t a l y group at post-treatment assessment (9.3 kg vs. 5.6 kg, respectively). Furthermore, at one-year follow-up, the dietplus-exercise group maintained significantly more weight loss than the diet-only group (7.9 kg vs 3.8 kg). Thus, exercise appears to promote long-term weight loss in obese NIDDMs, but part of this effect may be due to the nonspecific aspects of exercise, and fairly frequent exercise (3-4 times/week) may be required to maximize this effect. An additional post-hoc analysis in the Wing study corroborated the conclusions of other retrospective studies (33,36,42). Subjects in the two studies described above were divided into tertiles based on their selfreported Lxercise at 1 year (low = 168-616 kcallweek; medium = 700-1200 kcal/week; high = 1372-1446 kdweek). These tertiles were found to differ significantly in weight loss (2.3 kg, 5.9 kg, and 9.1 kg for low, medium, and high tertiles, respectively). Moreover, these tertiles differed significantly in their improvements of glycosylated hemoglobin, even independent of their magnitude of weight loss. One of the few studies that failed to find that dietplus-exercise produced better long-term weight loss than diet-only was a study by Hartwell et al. (32) with NIDDM patients. Seventy-six NIDDM patients were randomly assigned to a diet-only, exercise-only,dietplus-exercise, or an education control group. Weight changes at the end of the 10-week program were -2.5 kg, -0.7 kg, -0.24 kg, and +0.28 kg for the diet-only, exercise-only, diet-plus-exercise, and control groups, respectively. At six months of follow-up, overall longterm weight changes were -3.5 kg, -1.43 kg, -0.25 kg, and +1.0 kg, respectively. Although these results do not agree with the findings of most other studies regarding the beneficial effects of adding exercise to diet therapy, several features of the study should be noted. First, the diet-plusexercise group received only four supervised exercise sessions. Second, no increases in maximal oxygen consumption were noted in the diet-plus-exercise group. Since at baseline the subjects were characterized as sedentary, as indicated by their relatively low maximal


oxygen uptake (mean 22.4 mukg/min), an increase in Exercise Prescription Table 2 presents a summary of exercise prescripmean aerobic capacity following treatment should have tions used in the randomized trials discussed. Early occurred. Hence, the exercise intervention in the dietstudies lacked formal exercise prescriptions and a quanplusexercise group may not have been sufficient to protification of exercise performed is not readily available. duce a long-term weight loss effect. Therefore, these studies are not included in this table. More recent studies include formal exercise prescripType of Diet As noted above, the retrospective studies suggest tions; as seen in Table 2, these recent studies all use that exercise is important in maintaining weight regard- low- intensity aerobic exercise modalities. As shown, less of the type of diet (very-low-calorie diet or low- most studies stress walking with a Wuency of 3-4 days calorie diet) employed. 'Ihe mdomized trials confirm this. per week and a duration of about 30 minutes. Pavlou and associates (46)studied 160 police offiFew studies have systematically investigated the cers throughout eight weeks of active dieting and super- effects of different types or intensities of exercise used vised exercise and 18 months of follow-up. Subjects in combination with the diet on the long-term maintewere randomly assigned to one of four diets: a 1000 nance of weight loss. The only exercise variables k d d a y standard balanced calorie-deficit diet (BCDD), manipulated to date have been whether or not the exerinvolving regular foods; a lo00 k d d a y ketogenic pro- cise is supervised and the degree of choice allowed the tein-sparing modified fast consisting of meat, fish, and subjects. Craighead and Blum (17) compared superfowl; a liquid VLCD of 800 k d d a y , or a liquid VLCD vised exercise, non-supervised exercise, and a minimal of 420 kcdday. Within each of the four diet conditions contact condition in a sample of moderately overweight subjects were randomly assigned to either exercise or no women. The behavioral treatments for changing eating exercise. The exercise intervention consisted of habits were similar for all groups and lasted 12 weeks. walk/jog/run activities performed in three supervised The exercise interventions started in week five and consessionsper week at an intensity of 70% to 85% of max- tinued through week 12. Subjects in the supervised imal heart rate (HRmax)for a duration of 35-60 min- exercise group exercised three times per week for 40 utes. per session. Total weekly energy expenditure minutes, half pf which was at an intensity of 75% to Exercises included walking, jogging, calinduced by exercise was thus approximately 1500 kcal. 80% HR-. At the end of the 8-week treatment program, the BCDD- isthenics, stretching, and flexibility routines. In cononly condition (without exercise) had lost significantly trast,the nonsupervised exercise group signed a contract less weight than all seven other treatment conditions. to complete 90 minutes of exercise each week. These More striking, however, were the long-term effects. At subjects were free to choose whatever type of exercise 18-month follow-up, all groups that had participated in they preferred. The minimal contact group received supervised exercise had maintained their weight loss in similar information through written lessons and feedfull, regardless of the type of diet that was used. In con- back, attended no weekly meetings, but did sign an trast, all the non-exercise treatment conditions regained exercise contract at week 5. At the end of the 12-week significant amounts of weight, with an average weight program, both the supervised and contracted exercise regain of 74% of the initial weight loss. groups had lost significantly more weight than the miniExercise added to a VLCD-treatment protocol has mal contact group (5.4 kg and 3.8 kg vs. 1.6 kg, respecalso been investigated by others. Sikand and associates tively). During the one-year follow-up, the supervised (57) studied the addition of exercise to a VLCD pro- exercise group regained only 0.6 kg (1 1% of initial gram in 30 obese women. Exercise was supervised weight loss), while the exercise contract group regained twice weekly. The diet-only group lost 17.5 kg and the 1.8 kg (47.4% of initial weight loss). Consequently, at diet-plus-exercisegroup lost 21.8 kg of body weight by the one-year follow-up, overall weight loss of the superthe end of the four-month treatment program. At the vised exercise group was significantly greater (4.8 kg) end of a two-year follow-up, nearly all weight was than the exercise contract group (2.0 kg) or the minimal regained by the diet-only group (16.7 kg regain; 95.4% contact group (1.9 kg). Thus, in the only study on this of initial weight loss). In contrast, the diet-plusexercise topic, the supervised exercise program successfully group regained only 58.2% (12.7 kg) of their initial facilitated long-term maintenance of weight loss comweight loss. Thus, at 2-year follow-up, overall weight pared to the unsupervised exercise condition. Exercise has previously been divided into two loss was 0.8 kg for the diet-only group compared to 9.1 kg for the diet-plus-exercisegroup. types: programmed and lifestyle exercise (25). These studies suggest that the effect of exercise on Programmed exercise is the type of exercise which is the long-term maintenance of weight loss occurs irre- planned solely for the purpose of exercise. Lifestyle spective of the type of diet prescribed. exercise, on the other hand, is part of one's daily life, OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 593


e.g., walking from the parking lot to the office. To date there have been no studies that directly compared these two types of exercise. Closest to this is a study by Epstein and associates (26) in which overweight children aged 8-12 were randomly assigned to a diet-plusprogrammed-exercise intervention, a diet-plus“lifestyle-exercise’’intervention, or a diet-plus-calisthenics control group. In the programmed-exercisecondition, children elected to walk, run, bicycle, or swim three times per week at 60% to 75% of predicted HRma,. The “lifestyle” exercise program was isocalonc with the programmed exercise routine; children in this condition selected the type of exercise they wanted to perform from an exercise menu and no exercise intensity guidelines were applied. Hence, on a given day, the programmed exercise group might run a mile at a track while the lifestyle exercise subjects could elect to walk half a mile to school and back. The two treatment conditions thus differed primarily in their intensity of exercise and the degree of choice provided to the subjects. The three groups had similar weight changes over the initial 8-week program, again suggesting that a placebo exercise program (light calisthenics)

may produce results similar to more intensive exercise programs. However, at 2-year follow-up, the lifestyle exercise group maintained a significantlylower percentage of overweight (30%) than the programmed-exercise group (41%) or the calisthenics control group (42%). These results were interpreted as suggesting that the flexibility of the lifestyle intervention probably produced better exercise adherence and consequently better long-term weight loss. Most recently, a 10-year followup was conducted which showed that both the lifestyle and the programmed-exercise conditions maintained lower weight than the calisthenicscontrol (24). In Epstein’s program for obese children, an overweight parent participates as well and is prescribed all of the same behavior changes. Interestingly, the parents of the children in the study described above experienced equivalent weight losses in all conditions. Thus, the more flexible “lifestyle” intervention was not superior at 2 years for the parents nor did the groups differ at 10 years. The Epstein study (26) evaluated a more flexible exercise regimen, but did not really study “lifestyle defmed. It remains unclear intervention,” as typically --

Table 2. Summary Table of Exercise Prescriptions Used in Randomized Controlled Trials Evaluating the Role of Exercise on Long-Term Weight Maintenance *..

Reference

_________________________________Exercise Prescription____________________________________ Frequency Duration Supervision (YW Mode (dwk) Intensity 3

45-60

3

90

4

20

4-6

20-30

4

NR

3

60

3

60

walking

4

3 miles

Stretching, walking, jogging

5

25-50

Walking, jogging 3

25-45

Hartwell et al. Stretching, walking, jogging (32) Calisthenics, Pavlou et al. walk, jog, run (46) Perri et al. Stretching, walking, cycling (47) Perri et al. Not specified (but aerobic) (48) NR Sikand et al. (57) Wing et al. Calisthenics stretching (63) wallring

Wood et al.

(64) Wood et al. (65)

Additional Comments

60-70% HRmm 70-85% HRmax 60-70% HRRmax Not specified NR

Y (1 dlwk)

Not specified Not specified Not specified 60-80% HRmax

Y (2 dwk)

Study 1 “Placebo”

Y (2 dwk)

study 1

Y (3 dwk)

study 2

Y (3 dwk)

2 dlwk of NSE added at 3 months

60-80% HRmi3X

Y

Y N

Y (2 dwk)

Exercise added during maintenancephase

Y (2 dwk)

Group

HRmax = Maximal Heart Rate; HRRmax = Maximal Heart Rate Reserve; NR = Not Reported,NSE = Non-supervised exercise.

594 OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994


whether lifestyle exercise, such as using stairs rather than elevators, is indeed sufficient to make a long-term impact on body weight. This is an important question that should be empirically evaluated since lifestyle exercise is often recommended as part of behavioral treatment programs. As noted above, the studies of diet plus exercise have all used low-intensity aerobic exercise, usually walking (although subjects may be given the choice of including cycling or jogging in their exercise regimen). The emphasis has been on increasing the frequency and duration of exercise, rather than the intensity. This seems appropriate since high-volume, low-intensity exercise generates a substantial increase in energy expenditure while maintaining a low risk for exerciseinduced injuries (11,50). Moreover, low-intensity exercise may be just as effective as higher intensity exercise in preserving fat-free mass during periods of reduced energy intake (6). To date, no studies have evaluated the effects of strength training on the long-term maintenance of weight loss. Strength training has been shown to maintain fat-free mass (3) and muscular strength (4,39,52) during short-term active dieting, especially when the diet utilized is greater than 1000 kcaVday (3,22,23). However, whether this type of exercise promotes longterm weight maintenance remains to be examined. . . Mechanisms Underlying Long-Term Benefits of Diet Plus Exercise

The studies presented above clearly document that the combination of diet plus exercise promotes longterm weight loss compared to diet or exercise alone and show that subjects who report maintenance of an exercise habit have better long-term results. It is rare to see such consistency across the types of studies (correlational studies vs. randomized trials), across populations (ranging from children through adults) and across diet conditions (in very-low-calorie diets, as well as balanced diets). The important questions that now must be addressed are: (1) why is the combination of diet plus exercise more successful for long-term weight loss and (2) how can this effect be maximized. In truth, very little is known about why the combination of diet plus exercise is more effective for longterm weight maintenance. In order for weight loss to be maintained, it is necessary that some type of behavior change be maintained. However, there are few data available to indicate whether subjects treated initially in a diet-plus-exerciseprogram maintain their weight loss over time by maintaining changes in both diet and exercise or by maintaining changes in only one of these two behaviors. There are several possible ways in which the com-

bination of diet plus exercise is more effective than diet or exercise alone. First, it is possible that diet plus exercise act additively to produce caloric imbalance. Subjects in diet-plus-exercise interventions may make (and maintain) small changes in their energy intake (comparable to those in the diet-only group), and small changes in their energy expenditure (comparable to those in the exercise group), and these changes may be cumulative. As a result, the overall energy imbalanceof diet plus exercise may be greater than for either treatment alone, a notion supported by the results of Dahlkoetter et al. (19). A second possibility is that the combination of diet plus exercise produces compensatory effects. Adding exercise to a diet program may reduce the loss of lean tissue that results from moderate caloric restriction (5, 1 1,13,40), and may thereby lessen the dietinduced decrease in resting metabolic rate (27). Similarly, adding diet to the exercise intervention may help prevent the increase in food consumption that can occur with exercise (7,61). The combination of diet plus exercise also provides subjects with greater individual flexibility. Whereas patients in a diet-only group have the choice of restricting intake or not restricting intake, subjects in the dietplus-exercise gr6up may choose to diet or to exercise; moreover subjects may alternate between dieting and exercising at different times of the year. Thus, some subjects may maintain their weight loss by maintaining changes in diet and others by maintaining new exercise habits. Finally, diet and exercise interventions may act synergistically. The process of dieting, and the relatively quick weight loss that results, may make it easier for subjects to exercise; similarly, exercise may cause changes in appetite or in mood that make it easier to restrict calories or lead to selection of a lower fat diet. Increased physical activity has been shown to influence dietary intake in some (744) but not all studies (9). Likewise, exercise has been shown to increase feelings of general well-being (18), self-esteem (53) and mental vigor (60), and to reduce anxiety and depression (14, 49). Such beneficial effects may increase the likelihood of compliance to dietary protocols for weight reduction, and hence improve long-term weight control. To determine which of these mechanisms underlies the positive effectsof diet plus exercise vs. diet or exercise alone, it would be helpful to assess subjects’ intake and exercise as well as other parameters such as resting metabolic rate periodically throughout long-term weight control interventions. Unfortunately, however, current methods for assessing intake and exercise, with the possible exception of doubly-labelled water (51,56) may not be sufficiently accurate to detect the small differOBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 595


ences in these parameters that over time result in the better long-term weight loss outcomes. The only long-term data that are relevant were reported by Wood et al. (65). In a study described above, these researchers compared diet-only vs. dietplusexercise and found that men in the latter group had a 3.6 kg greater weight loss at one year. Men in the diet-only condition reduced their intake by 729 k d d a y vs. 592 kcal/day in the diet-plus-exercise group. Moreover, men in the diet-plus-exercisegroup reported walking about 2 km/d; using data in this article we estimate that these men were expending 150-200 k d d in their exercise. Unfortunately no data on exercise level in the diet-only condition are given. If it is assumed that the diet only group was doing no additional exercise and that resting metabolic rate and energy expenditure in other exercise during the day were comparable in the two conditions, the diet-plus-exercise group is found to be 20-70 kcdd below the diet-only group. This difference, if it is closer to the 70 k c d d end and is maintained over a full year, could produce the 3.5 kg differential in weight loss. These data are presented in part to show the type of analysis that could help to illuminate the mechanisms underlying the diet-plus-exercise effects but also to illustrate the difficulty that will occur in trying to provide such data with current measurement techniques. Maximizing the Effects of Diet Plus Exercise on LongTerm Weight Loss The other important question is how best to maximize the effects of the combination of diet plus exercise on long-term weight loss. The answer would seem to depend on determining what types of diet, exercise, and combination will produce the best long-term adherence. In order for any exercise to have an effect on long-term weight loss, the exercise must frrst be performed, i.e., the degree of adherence to exercise would appear to be a more important determinant of overall caloric expenditure than other variables such as the number of calories burned in exercise or the effect of exercise on resting metabolic rate or lean body mass. Similar reasoning applies to the diet. Unfortunately, we know very little about the characteristics of the diet or exercise regimen that will improve long-term adherence. Research is needed that compares the behavior changes and long-term weight losses that occur with different types of diet (such as in study) and different types of exerthe Pavlou et al. ([46] cise. As noted earlier in this review, comparison of aerobic and resistance exercises is needed. It is also important to compare different types and intensities of exercise, different degrees of flexibility in the exercise regimen, and different behavioral approaches to promoting 596 OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994

exercise adherence (such as contingency contracting procedures). Blair et al. (10) has suggested that dividing the exercise regimen into several small periods of exercise (e.g., prescribing 3 periods of exercise, each lasting 10 minutes rather than 1 period of 30 minute duration) may improve adherence. DeBusk and associates (20) found that this type of exercise regimen could produce significant improvements in cardiovascular fitness, but the effects of shorter vs. longer bouts of exercise on adherence and weight loss have not been examined. Variables such as exercising at home vs in supervised group sessions also deserve further attention. King et al. (38). in a year-long study of exercise in a community-based sample of older adults, found that exercise adherence was better in a home-based program than in a group-based program. The exercise intensity had of the home-based program (80% vs 60% HR), far less impact on adherence. However, the relevance of these findings to the present analysis is unclear, as most of the participants in King’s study were normal weight and the intervention included exercise only (not diet plus exercise). Moreover, at the end of the year-long study, none of the groups in King’s study differed from a no-treatment control condition in weight loss or body composition. In contrast, Craighead and Blum (17), in a study digussed above, found that initial use of a groupbased supervised exercise improved long-term weight ’loss compared to the contract condition, where subjects exercised on their own. Further studies comparing interventions such as these are needed to determine whether the benefits of diet and exercise for long-term weight loss can be increased by varying the type of diet or exercise regimen that is prescribed. Another approach to maximizing the benefit of exercise for long-term weight maintenance is to focus on exercise during the maintenance phase, instead of or in addition to during the initial treatment. Since the greatest benefit of exercise appears to be for the maintenance of weight loss, exercise may be particularly useful as a maintenance strategy. To test this, Perri et al. (48) randomly assigned 91 moderately overweight subjects to one of five groups. All groups received the identical 20 week weight loss intervention, but they differed in the type of maintenance intervention that was provided. Group 1, the control condition, received no maintenance intervention; group 2 received bi-weekly contact for the next 18 months; group 3 was seen bi-weekly and given a social influence intervention; group 4 was seen biweekly and participated in an exercise intervention; and group 5 was seen bi-weekly and given both the social influence and exercise intervention. Subjects in the exercise conditions were encouraged to gradually increase their exercise to 30 minutes per day, 6 days per week, and participated in group exercise session at each


bi-weekly meeting. Weight losses at the end of the 18month follow-up period were 3.6, 11.4, 8.4, 9.1, and 13.5 for the five groups, respectively. The four groups given maintenance interventions all lost significantly more weight than the control group (group l), but the differences among groups 2-5 were not statistically significant. Thus, the degree of contact provided, rather than whether or not exercise was further emphasized, seemed important in long-term weight control. The failure to find an effect of the exercise intervention on longterm weight loss may well have been due to the fact that attendance at the exercise sessions was poor, and that self-reported overall activity levels at 18 months did not differ for the groups prescribed exercise vs. those not prescribed exercise. However, when the data were analyzed across all five groups, there was a marginally significant relationship between self-reported exercise and weight loss, a finding that replicated the results of the numerous correlational studies described above. Thus, efforts are needed to develop strategies to promote longterm adherence to exercise, but the use of a maintenance program with bi-weekly exercise sessions may not be the best approach to increasing long-term exercise adherence.

Based on these few studies, treatment with exercise alone does not appear to be particularly effective for long-term weight loss. However, before reaching a definitive conclusion that exercise alone is not a useful approach for long-term intervention, we feel that further investigation is needed. The characteristicsof the exercise prescribed may affect long-term weight losses not only in diet-plus-exerciseprograms, but also in interventions using exercise alone. Moreover, weight lost through exercise may be easier to maintain than weight lost through diet. As noted above, King et al. (37) found that a simple maintenance intervention of mailings and phone calls was successful in maintaining weight lost through exercise, but not weight lost by diet only. Unfortunately, this study did not include a dietplus-exercise condition so it is not known how weight maintenance in the exercise-only condition would compare to a diet-plusexerciseprogram.

Conclusion Based on the randomized studies presented above, it appears that subjects who are initially treated in a weight loss program that combines diet plus exercise have the best long-tern weight loss results. The correlational studies add to this, suggesting that subjects who Identifying Individual Differences in the Response to are most successful at maintaining their weight losses are those who continue to exercise. Thus, exercise Diet Plus Exercise Not only is it important to determine how to dappears.to be a key wmponent for weight loss maintfmnm. However, at present we know very little about the mize the effectiveness of diet plus exercise, but also to determine whether there are subgroups of the obese mechanisms underlying this effect. Further research populations who respond best to this combination. As focused on the long-term changes in energy balance noted above, data from Wood et al. (66) showed that produced by the combination of diet plus exercise is men lost more weight when treated with diet plus exer- clearly needed. It is also important that we understand cise than with diet alone, whereas for women these two more about the subject characteristics,the types of diets, different interventions produced comparable weight and the types of exercise that maximize the positive losses. Other studies have shown that exercise is partic- effects of diet plus exercise. To date, no studies have ularly effective in reducing android obesity, perhaps been conducted on when to introduce exercise in a dietexplaining the above gender difference (11,12). Other plus-exercise program. Perhaps it would be best to subject characteristics such as the degree of obesity, the introduce diet fust,and to teach participants to exercise level of insulin resistance, and age of the subject may only after initial weight loss is achieved. The best longalso influence the response to diet plus exercise (12). term weight loss most likely occurs when adherence to Older subjects with more medical problems have been diet and exercise is maintained, so that the question of shown to have greater difficulty adhering to an exercise maximizing long-term weight loss may well translate program (58) and thus the combination of diet plus exer- into a question of maximizing long-term adherence to cise may be particularly effective in younger, healthier diet, and especially to exercise regimens. Thus, longsubjects. It would also be interesting to know whether term weight losses might best be improved by research baseline activity level of the participant is related to the focusing on how best to get overweight individuals to adhere to diet and exercise - long term. effectiveness of diet-plus-exercisevs. diet-only. How Effective f o r Long-Term Weight Loss Is Exercise Alone? In the above review, we have described the very few studies which have compared diet only, and diet plus exercise to treatments involving exercise only.

Acknowledgments This manuscript was supported by NIH grant DK29757 and NHLBI grant HL41330 to Dr.Rena R. Wing.

OBESITY RESEARCH Vol. 2 No. 6 Nov. 1994 597


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