In this weight loss intervention study, we found that the amount of weight regained during follow-up was associated with the magnitude of change in objectively measured PAEE during weight loss. Specifically, the greater the decrease in PAEE during the 5-months of energy deficit, the greater the weight regain during follow-up. The amount of weight regained was related to the decrease in PAEE even after adjustment for the amount of weight loss during intervention. Conversely, weight regain was not associated with decreases in RMR during the weight loss intervention.
Although it has been suggested that physical activity inversely affects body weight, to our knowledge, no previous study has examined whether a decline in PAEE (either measured objectively or by self-report) during periods of energy deficit is a factor predictive of future weight regain. However, a few studies have examined the effect of changes in self-reported physical activity after
a weight loss intervention on weight regain. One study found that increases in physical activity measured by a questionnaire during a 2-year period after a weight loss program was a protective factor, and was among a group of variables related to the amount of weight regain (10
). Another study found less exercise time (sports and other activities) and more television/computer time accompanied weight regain during the 2-year follow-up after a 9-month weight loss intervention in adolescents (20
). Other studies have also shown high levels of self-reported physical activity after weight loss are associated with less weight regain (12
). Also, integration of walking into a weight maintenance program decreased the amount of weight regain 2 years after weight loss compared to controls (6
). These studies point to the importance of physical activity in reduced-weight individuals trying to maintain their weight loss. Our data, however, showed the magnitude of weight regain during follow-up was associated with decreases in an objective measure of physical activity during a period of energy deficit. Interestingly, weight regain was not related to self-reported physical activity during follow-up, possibly due to inconsistencies of self-reported data and the scale’s inadequate sensitivity to change over a period of time for this sample of women. Thus, whatever the mediating factor, these results do suggest that maintaining a higher level of physical activity during a weight loss treatment is important for prevention of weight regain.
There are conflicting data regarding whether differences in baseline RMR or changes in RMR with weight loss are predictive of weight change. Ravussin et al. found that Pima Indians with a lower RMR gained more weight over a 4-year period (19
). However, data from the Baltimore Longitudinal Study on Aging showed weight change during a 10-year follow-up was not related to individual RMR (24
). Weinsier et al. also found lower RMR after weight loss was not predictive of greater weight regain after 4 years (32
). Pasman et al. examined the association between changes in RMR induced during a 2-month low energy diet and weight regain during 14 months of follow-up in obese, premenopausal women (17
). They found that the amount of weight regained was greater in women with a greater decrease in RMR. In contrast, in our study, weight regain was not associated with weight loss-induced changes in absolute RMR, or RMR relative to lean mass or fat mass. The study by Pasman et al. and ours induced a similar amount of weight loss, however, in our study, the weight loss intervention was longer, the decrease in RMR appeared less, and our participants were older.
Our study showed that most of the women experienced a decrease in PAEE and absolute RMR during weight loss, with an average decline on the order of 26% and 7%, respectively. Other studies that have directly measured PAEE or derived non-resting EE from a measure of total EE, have also found that these components of EE decline during negative energy balance induced by exercise training (14
) or a hypocaloric diet (1
). In our study, PAEE decreased in all groups, even when calories expended during exercise sessions were included in total PAEE (changes in PAEE: −444.0 ± 635.6 kJ/day for DIET+EX-LO, −357.2 ± 620.9 kJ/day for DIET+EX-HI, and −498.3 ± 551.9 kJ/day three groups combined). The amount of weight regain after 6- and 12-month follow-up was also related to changes in total PAEE (r = −0.518, p = 0.002; and r = −0.429, p = 0.011, respectively). Therefore, it appears that PAEE outside of the exercise program (i.e. spontaneous physical activity), decreased to a greater level than the increased EE resulting from purposeful exercise as part of the intervention. PAEE relative to lean mass or body weight also decreased, suggesting that the decrease in EE due to daily physical activity was not solely accounted for by a reduced body mass. Furthermore, it is the decrease in PAEE itself, beyond variation in weight loss, that predicts future weight regain, as evidenced by the fact that the amount of weight loss did not affect the relationship between PAEE decrease and weight regain. Additionally, the fact that the DIET+HI-EX group showed a strong association between PAEE decrease and weight regain, suggests that exercise intensity during weight loss intervention may affect the rate of weight regain by altering PAEE.
Likewise, our RMR results confirm other studies that show a decrease in RMR with dietary-induced weight loss (1
). However, our data showed that, when adjusted for lean mass, there was no change in RMR, suggesting that the decrease in RMR was accounted for by the loss of lean mass. This is consistent with some studies showing the decrease in RMR after weight loss was not beyond the expected reduction for the amount of lean mass lost (31
Mayer and coworkers hypothesized that, in sedentary persons, there is a threshold of physical activity below which leads to obesity (13
). Schoeller et al. further examined this threshold hypothesis in women. They found that previously obese women whose physical activity was great enough to increase total EE to RMR ratio (TEE:RMR, or physical activity level) above 1.75 were less likely to regain weight than those less active women (TEE:RMR <1.75) (21
). They subsequently provided a structured exercise program to a subset of these less active women to increase TEE:RMR to 1.75, and their weight gain was stopped for the duration of the program. In a study by Weinsier et al., women who were successful at maintaining lost body weight had a TEE:RMR of around 1.7 before and after weight loss intervention, while those gaining weight had a value of 1.55 and 1.60, before and after the intervention (30
). We calculated TEE:RMR (considering thermic effect of food is approximately 15% of TEE, TEE = [RMR + total PAEE]/85%) at the end of weight loss intervention. The mean TEE:RMR was 1.58 (± 0.12), with 6 of the 33 women having levels greater than 1.70, and only 2 of them greater than 1.75. Since most women regained weight during follow-up, our results appeared to support this threshold hypothesis.
In summary, our study found the magnitude of weight regain during follow-up was associated with decreases in PAEE during weight loss in women, thereby suggesting the importance of maintaining a high level of daily physical activity to mitigate weight regain after weight loss. Given the mean PAEE decreased even when calories expended during prescribed exercise were included, physical activity outside of structured exercise programs may be a more important factor in prevention of weight regain. Therefore, behavioral strategies to minimize this decrease should be integrated into weight loss interventions to help with maintenance of weight loss.