To our knowledge, this study provides the first detailed results on the association between PA and weight loss maintenance in a large population-based sample of premenopausal women throughout the United States. Furthermore, our definition of successful weight loss maintenance brings novelty owing to its relativity to baseline body weight and percent of lost weight, as opposed to generalizing an absolute number of weight losses onto all the participants of heterogeneous baseline weights, as seen in other studies (4
). Approximately 20.5% of the women successfully maintained their intentional weight loss, defined as intentionally losing >5% of body weight and having regained no more than 30% of their weight loss (or 1.5% of their baseline 1989 weight) over 6 years. Although diet is an important aspect of the energy balance equation, studies have shown that exercise may be a stronger determinant than diet for long-term weight loss maintenance (25
). We observed that overweight and obese women who increased their activity level were more likely to regain less body weight than their peers. Also, for 30 min/d increase in exercise duration, jogging or running appears to be the most protective type of activity against weight regain. Non-brisk walking was only protective among women who were overweight or obese. Women who sustained or increased to ≥30 min/d of total discretionary PA were more likely than their peers to maintain the lost weight for 6 years, as were women who sustained ≥9 MET-Hours/week of walking (~3 hours/week of average-pace walking), and women who sustained 30+ min/d of moderate-to-vigorous activity. However, among sedentary women, PA increase had to exceed 30 min/d to be beneficial and a significant dose-response relationship with less weight regain was evident. In addition, there was an independent association between decreased TV viewing and reduced risk of weight regain.
The rationale for choosing 5% as the minimal magnitude of weight reduction was because this level is regarded as a clinically significant change, particularly in terms of weight loss (27
) and in terms of reduction of risk factors of diabetes and heart disease (28
). The rationale for choosing a cut off of 30% of the lost weight (or 1.5% of baseline weight) is because the literature shows that advancing years is inevitably accompanied with weight gain, even for those who maintain a steady exercise schedule (25
). Hence, if we were to be stringent in our weight loss maintenance success definition and we were to allow 0% regain of the lost weight, only 11.95% of our sample would be successful maintainers (n=545) as compared to our current maintainers (20.49%; n=934).
Our data showed that higher PA levels were important for preventing weight regain. This is concordant with other studies showing that successful weight loss maintainers reported engaging in activity as part of their behavioral treatment program (4
). Nevertheless, modest age-associated weight regains were still observed in our cohort, suggesting that maintenance of long-term weight loss appears to require increased exercise with aging. This is consistent with Jeffery and colleagues (26
) who found that even relatively high PA levels may not be sufficient to protect against any weight regain. In our cohort, the estimated amount of total discretionary PA required to prevent any weight regain (zero weight regain) varied between 3.2 hours/d for lean women and 2.3 hours/day for overweight/obese women. Although few people would be willing to engage in that activity level, which is typical of many traditional lifestyles, lower amounts of activity were sufficient for women to maintain their weight loss and more moderate amounts of activity appear to have some benefits. In our cohort, while 9% of the women who maintained their body weight after 6 years reported using exercise and diet as a mean of long-term weight loss maintenance, only 0.5% of them reported using exercise alone without diet.
For clinical and public health approaches to weight control, it is commonly accepted that an energy expenditure of 150 kcal/d (~20 min/d of activity) is needed; yet there is little empirical evidence to support this speculation (26
). Over time, PA guidelines have changed substantially. In 1996, the Surgeon General’s report emphasized the health benefits of engaging in moderate levels of PA (sufficient to burn 150 calories per day), such as 30 min/d of brisk walking (30
) and the NIH consensus development panel advised a regular performance of 30 min/d of moderate PA to maintain the different health benefits such as coronary vascular disease prevention (31
). In 2001, Wing and Hill found in a study of 3000 subjects (average 45 years) in the National Weight Control Registry that successful weight loss maintainers who lost at least 17 kg for at least 1 year exercised for about 1 hour/day; however the denominator for these successes is not known. According to the 2008 Dietary Guidelines, at least 60 to 90 minutes of daily moderate-intensity activity are needed while not exceeding caloric intake requirements to sustain weight loss (32
). Our study, however, observed that PA increase to at least 31–60 min/d was necessary for weight loss maintenance over the 6-year follow-up, and participants who reduced their PA regained weight. Our findings are consistent with other studies (8
). Our results also showed that even higher increases (>30 min/d) were needed among sedentary women, similar to Jakicic and colleagues (34
) who reported that an average PA increase by 30 to 40 min/d improved long-term weight loss maintenance in women who were overweight and sedentary. Moreover, Schoeller et al (5
) found that an average of 80 min/d of moderate activity or 35 min/d of vigorous activity was needed to minimize weight regain in sedentary women. Additionally, our results indicate that greater increases in discretionary activity are needed among sedentary women who are trying to maintain weight loss than sedentary women who are trying to prevent weight gain (35
). One possible explanation to why more min/d are needed for prevention of weight regain than for weight gain is that subjects with chronic excess weight may experience metabolic alterations, and may thus require more effort to achieve a substantial weight loss (36
Although the American Dietary Guidelines recommend 60–90 min/d of PA to sustain weight loss, some adults may be discouraged by the 90 min/d recommendation and thus may not engage in any activity. Fogelholm and colleagues (37
) showed that poor long-term adherence may be related to an overly time-consuming program. In our analysis, it appeared durations less than 60 to 90 min/d will on average still have benefit and will be sufficient to sustain weight loss. Furthermore, consistently with other longitudinal studies (25
), our results showed the benefits of activity increase in 1997, independent of baseline activity, were more than twice as high among overweight women; our results also indicated that baseline activity was not associated with 6-year weight regain prevention, similar to what we previously found with 8-year weight gain prevention (35
Congruent with our findings that increased television watching was positively associated with weight regain, a substantial body of evidence suggested that reductions in TV viewing would result in decreases in BMI or prevalence of obesity in adolescents(39
). Importantly, the effects of sedentary behavior appear to be independent of active physical activity, suggesting that weight control programs should address both of these dimensions.
There are several limitations to the present study. First, the full set of PA questions was not included on the 1993 and 1995 questionnaires; thus it is not known when during the interval activity levels changed, nor for how long the actual change was maintained. Second, there may be other types of activities such as weight training or sleep that could have an impact on body weight, we could not account for these variables because they were not included in all of our questionnaires. Also, our measurements of PA were inevitably imperfect, which will have tended to underestimate the benefits of PA and overestimate the amount of PA needed to prevent weight gain; however, this has not prevented epidemiology from identifying the importance of PA and disease in a variety of prospective cohort studies. While objective measures of PA may have been desirable, they too have error, and good validity of our PA questions has been documented (16
). Third, we cannot be sure that all the weight loss between 1989 and 1991 was intentional as 1993 was the year when measures of intentional weight loss were collected; however, a strong reason that this was most likely intentional is that participants were relatively young, healthy, and they needed to be alive and respond in 1997. Fourth, dietary intake was not assessed in 1997, the follow-up year for determining change in PA and weight. However, in this analysis, excluding the dietary variables from the models did not meaningfully affect the results. Fifth, the sample was not a random sample from the United States. Moreover, we did not include women who were pregnant or recently pregnant. Thus it is not clear whether these results can be generalized to pregnancy-related weight gain; however, this relationship is more complicated and deserves a separate investigation, as discussed elsewhere (6
Despite these limitations, our study has several strengths. First, it included a large sample of women who were followed with repeated assessments over a 6-year period. Second, the prospective design allowed us to assess the activity exposure before the weight changes’ outcome. Third, we were also able to control for sedentary behavior by measuring the total number of TV watching hours. Moreover, information on a wide variety of potentially confounding behavioral and demographic variables was collected at each assessment, which allowed us to assess activity patterns and weight change associations independent of these potential confounders. Fourth, despite the different weight loss maintenance definitions in the literature in terms of both, weight loss magnitude and maintenance duration, our continuous outcome of weight change represents a sensitivity analysis justifying our criteria when defining weight loss maintenance as a dichotomous outcome. Parallel to Wing and Hill’s definition(40
) of intentionally losing at least 10% of body weight and keeping it off for a year, we defined our outcome as losing >5% of body weight and keeping it off for 6 years while remaining within 30% of weight loss (or 1.5% of initial weight). Finally, we were able to exclude women with conditions affecting weight, such as pregnancy-related or post-delivery weight gain.
Our prospective study indicates that a high PA level is needed to maintain an intentional weight loss. At least 30 min/d of moderate-to-vigorous PA are needed to prevent regaining >30% of weight loss; however, a larger increase (by at least 31–60 min/d) may be needed in sedentary women to improve weight loss maintenance. Adults who are unwilling to increase their activity level substantially should be reminded to reduce caloric intake and to engage in PA to prevent weight regain. Adults of any weight should increase their exercise as they age to prevent weight regain after weight loss.