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Prescribing physical activity to prevent weight gain

This is an excerpt from Physical Activity and Obesity - 2nd Edition by Claude Bouchard & Peter Katzmarzyk.

Amount of Physical Activity to Prescribe

Recent recommendations suggest that individuals should perform 30 to 60 min per day of moderate-intensity physical activity to prevent weight gain, but a higher level—60 to 90 min per day—to prevent weight regain. These goals for weight regain prevention are based on randomized clinical trials and on studies evaluating successful weight loss maintainers. Each of these types of studies is discussed next.

Randomized Clinical Trials

Physical activity is recognized as a critical aspect of behavioral weight control interventions. Typically, behavioral weight control programs have encouraged participants to gradually increase their activity until they achieve a level of at least 1000 kcal/week of moderate-intensity physical activity. This level of activity would equate to approximately 10 miles of brisk walking per week and would take about 150 min per week to complete. The 150 min per week exercise goal has been adopted in several large weight loss trials such as the Diabetes Prevention Program (2).

Recent studies suggest that higher levels of physical activity may be more beneficial for weight loss maintenance, raising concerns about the typical exercise prescription. Jakicic and colleagues found that women who reported doing over 200 min per week of activity (about 2600 kcal/week) at 6, 12, and 18 months had better weight losses at all time points than those reporting exercise durations of

To test this empirically, Jeffery and colleagues (6) randomized obese individuals to behavioral weight loss programs that included exercise prescriptions of 1000 kcal/week (standard behavior therapy group) or 2500 kcal/week (high physical activity group). Both groups were placed on a low-calorie, low-fat diet and participated in group classes addressing behavioral weight control strategies. There were no differences in weight loss between the 1000 kcal and the 2500 kcal exercise group at six months, but the high exercise group maintained their weight losses better from 6 to 12 months and achieved greater overall weight losses at 18 months (4.1 vs. 6.7 kg [9 vs. 14.8 lb]; see figure 60.1).

Although treatment contact was terminated at 18 months, all participants were reassessed at 30 months. At month 30, weight losses of the 1000 and 2500 kcal groups were 0.90 and 2.86 kg (2 and 6.3 lb), respectively, and did not differ between groups. The failure to find better maintenance of weight loss in the high exercise group resulted in large part from the failure of these participants to maintain their high doses of physical activity. Comparisons of participants who maintained physical activity levels of 2500 kcal/week or greater at month 30 with those who reported lower levels of activity (6 kg (13.2 lb). Finally, these investigators examined the effect of consistently exercising at high levels. Those who reported >2500 kcal/week in physical activity at 12, 18, and 30 months (N = 13) were compared to all other participants. The high exercisers maintained weight loss of 12 kg (26 lb) at 30 months, compared to 0.8 kg (1.8 lb) in the other participants. While such consistently high levels of activity are associated with impressive long-term weight losses, it is clearly difficult for most obese patients to achieve and maintain these high doses of activity. Moreover, these participants reported not only high exercise levels, but also significant decreases in energy intake and dietary fat intake. Thus, their successful weight loss maintenance probably related to their overall pattern of positive behavior changes.

National Weight Control Registry

The National Weight Control Registry (NWCR) provides further evidence that weight loss maintainers are characterized by high levels of physical activity. The NWCR was established in 1993 to investigate the characteristics of individuals who have succeeded at losing at least 30 lb (13.6 kg) and keeping it off at least one year. Currently there are over 5000 individuals in the registry. These members far exceed the minimum eligibility criteria; on average they have lost almost 70 lb (32 kg) and kept it off almost six years. Analyses of approximately 3000 registry participants indicate that the average participant reports 2691 kcal/week (7) in physical activity. Men report higher levels of activity than women (2903 vs. 2532 kcal/week), but the average level corresponds very well with current activity recommendations for weight loss maintenance. However, it should be noted that there is marked variability among NWCR participants; 25% report expending

A recent analysis of registry members suggests that walking is the most commonly reported activity (8). Resistance training is the next most popular activity; cycling, use of cardiovascular exercise machines, aerobics, and running are other commonly performed activities.

When followed over a year, registry members experience an average of a 2.1 kg (4.6 lb) weight regain. One-year weight regain has been associated with demographic variables (higher age, greater weight loss, shorter duration of weight loss maintenance) and with adverse changes in eating and exercise behavior. Of particular relevance is the fact that decreases in physical activity (independent of demographic variables and other behavior changes) are significantly associated with increased risk of weight regain. Likewise, those individuals who not only decrease their activity, but also relapse in other behavior changes (e.g., both decreasing activity and increasing their television viewing), experience larger weight regains (9).

Comparison of Successful Weight Losers and Normal-Weight Controls

There are several limitations to the registry, including the use of self-report measures of physical activity and the inability to determine whether the level of activity associated with prevention of weight gain differs from the level associated with prevention of weight regain. To make this direct comparison, we (10) identified 135 women who had reduced from overweight or obese to normal weight, and who had lost at least 10% of their body weight and kept it off for five years. Thus the criteria used to define weight loss maintainers in this study were far more strict than those used in the NWCR. These individuals were compared to 102 always normal-weight women, who were weight stable and had no history of ever being overweight. Both groups were asked to wear RT3 triaxial accelerometers for one week, and comparisons were made of the number of minutes (using 10 min bouts of activity) spent in low-intensity (2 to 2.9 metabolic equivalents [METs]), medium-intensity (3.0 to 4.9 METs), or high-intensity (≥5.0 METs) activity.

The weight loss maintenance group spent more minutes per day in medium- or high-intensity activity (average of 58 vs. 52 min/day) than the always normal-weight controls, with the difference particularly apparent for the minutes of high-intensity activity (24.4 vs. 16.9 min/day, p < .02). Moreover, in the always normal-weight group, 56% reported 30 to 60 min/day of moderate- or high-intensity activity and 30% reported >60 min/day. This contrasted with data for the weight loss maintenance group, among whom 32% reported 30 to 60 min/day but 44% reported >60 min/day. These findings are consistent with the suggestion that 30 to 60 min/day of activity is needed to prevent weight gain, but that a higher level, 60 to 90 min/day, is required to prevent weight regain (see figure 60.2). Of note, however, these data indicate that both duration and intensity may be related to successful weight loss maintenance.

Conclusions

There is consistent evidence that weight loss maintenance is enhanced by ongoing adherence to physical activity. However, the reasons for this relationship are not clear. One possibility is that those who are maintaining high levels of physical activity are also maintaining improvements in diet and eating behaviors, and that this overall pattern of adherence (rather than exercise per se) relates to long-term weight loss maintenance.

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