Is regular exercise an effective strategy for weight loss maintenance?

Abstract

Weight regain after weight loss is one of the most significant challenges to successful obesity treatment. Regular exercise has long been touted as a strategy for weight loss maintenance, but the lack of clear evidence in clinical trials has caused some to question its effectiveness. In this review, we present the arguments both questioning and in support of exercise as an obesity therapeutic. Our purpose is to bring clarity to the literature, present a unified perspective, and identify the gaps in knowledge that need to be addressed in future studies. Critical questions remain including sex differences, individual variability and compensatory behaviors in response to exercise, exercise adherence, the role of energy flux and the molecular mechanisms mediating the beneficial effects of exercise after weight loss and during weight regain. Future research should focus on these critical questions to provide a more complete understanding of the potential benefits of exercise on weight loss maintenance.

Keywords: Individual variability; Obesity; Physical activity; Weight regain.

Fig. 1

The energy gap The energy gap is represented with data from MacLean et al. Am J Physiol Regul Integr Comp Physiol, 2009. 297(3): p. R793–802 [11]. Energy intake and expenditure are displayed for obese-prone, male, Wistar rats under three different conditions. First, in the obese state following 16 weeks of ad libitum feeding on a high fat diet (Research Diets Inc. D12344). Second, after calorie-restricted weight loss on a low fat diet (Research Diets Inc. D11724) to yield a 10–15% body weight reduction. Third, upon ad libitum refeeding on a low fat diet during the first day of relapse. The energy gap, defined by the mismatch between appetite and energy requirements following weight loss, is apparent during this ad libitum refeeding phase. This mismatch between the calories desired and calories required establishes a strong and persistent biological pressure to regain lost weight.

Fig. 2

Impact of Weight Loss and Exercise on the Energy Gap The energy gap is a term used to describe the mismatch between appetite and energy requirements, expressed in energy equivalents. There are numerous adaptations to weight loss that culminate in an elevated appetite and suppressed energy expenditure, which drive weight regain. Some of the adaptations contributing to the energy gap are displayed in the left panel including: changes in hypothalamic neuropeptide expression and decreases in sympathetic nervous system (SNS) tone, resting energy expenditure, oxidative capacity, insulin, leptin, and circulating nutrients. Exercise counters many of the adaptations to weight loss and can attenuate the energy gap in a tissue specific manner including: increases in SNS tone, hepatic de novo lipogenic capacity, skeletal muscle dietary fat oxidation, circulating glucose and free fatty acids. An exercise signal has yet to determined, however, given the complexities of the exercise response it is unlikely we will find a single hormone or factor that is responsible for the effects of exercise on the energy gap. Abbreviations: neuropeptide Y; NPY, pro-opiomelanocortin; POMC, sympathetic nervous system; SNS, resting energy expenditure; REE, gastrointestinal; GI, free fatty acids; FFA, triglycerides; TG, de novo lipogenesis DNL, calcium; Ca, brain-derived neurotrophic factor; BDNF, interleukin-6; IL-6.

Fig. 3

The role of energy flux on appetite Energy balance (black diagonal line) can be achieved at various levels of energy flux (turnover) so long as energy intake is match to energy expenditure. Weight loss maintenance following calorie restriction is often characterized by a low flux state (low energy intake and low energy expenditure). In this low flux state, there is a large mismatch between appetite (red dashed line) and energy requirements. This large energy gap commonly results in overfeeding and weight regain. Exercise can be used to shift a weight-reduced individual into a higher flux state. The high flux state increases energy expenditure and decreases appetite to minimizes the energy gap [67]. This closer matching of appetite with energy requierments can minimized the drive to regain lost weight and improve weight loss maintenance. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

Sex differences of exercise on weight regain Female body weight in the weight-reduced state and during the early stages of weight regain (B) are compared to data from males (A) that are published in MacLean et al. Am J Physiol Regul Integr Comp Physiol, 2009. 297(3): p. R793–802 [11]. In both cases, obese-prone, Wistar rats were fed a high fat diet (Research Diets Inc. D12344) for 16 weeks prior to calorie-restricted weight loss on a low (males) or medium (females) fat diet (Research Diets Inc. D11724 & D07091301, respectively). Following a 15% reduction in body weight, rats were maintained at the lower body weight for 8 weeks to minimize the acute response to weight loss. At the end of 8 weeks, rats were allowed to refeed ad libitum for 8 weeks. Rats were randomized to forced treadmill exercise (EX) training (15 m/min, 1 h/day, 6 days/week) or sedentary conditions (SED) at the time of weight loss and continued EX or SED conditions for the remainder of the study. The red dashed line denotes the body weight of the males and females in the obese state (prior to exercise and weight loss). These studies were approved and carried out in accordance with the institutional review committee. *indicates significant (p < 0.05) differences between EX and SED groups. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Sex Differences in the Energy Gap in Response to Exercise The energy gap in respose to exercise in females is compared to data from males published in Steig et al. Am J Physiol Regul Integr Comp Physiol, 2011. 301(3): p. R656–67 [60]. Energy intake and expenditure in male (A) and female (B) Wistar rats in the obese state after 16 weeks of high fat diet (Research Diets Inc. D12344) feeding and during the first day of ad libitum refeeding on a medium fat diet (Research Diets Inc. D07091301). Refeeding took place following calorie restricted weight loss to achieve a 10–15% reduction in body weight and 6–8 weeks of weight loss maintenance. At the time of weight loss rats were randomized to forced treadmill exercise (EX) training (15 m/min, 1 h/day, 6 days/week) or sedentary conditions (SED). The energy gap identifies the difference between appetite (energy intake) and energy requirements (energy expenditure) during the first day of refeeding. A third group of sedentary males (sedentary gap matched) did not refeed ad libitum but were provided calories sufficient to achieve an equilavent positive energy balance to that of the exercised males. These studies were approved and carried out in accordance with the institutional review committee. Abbreviations: EE; Energy Expenditure.