ASN Community Forum
Both biological and behavioral factors pose substantial obstacles to achieving energy balance at a reduced body weight. During weight loss, total daily energy expenditure (TDEE) declines due to decreases in resting energy expenditure (REE) and physical activity energy expenditure (PAEE) that result primarily from the reduction in body mass. Furthermore, some evidence suggests that weight reduction is accompanied by an enhancement in metabolic efficiency that leads to a greater than expected reduction in TDEE for the change in body mass. To compensate for this reduction in TDEE and avoid weight regain, a permanent behavior change that leads to a lower energy intake (EI) and/or a higher level of energy expenditure (EE) through physical activity (PA) must occur. Furthermore, some evidence suggests that REE after weight loss is reduced to a greater extent than predicted (i.e. adaptive thermogenesis, AT) and that AT persists long-term (1-6 years). However, other studies have found no evidence of AT during weight loss or suggest that it resolves during sustained weight loss maintenance. We will provide some mechanistic insights from rodent studies as well as present data from human observational and randomized controlled studies from others who have investigated the energetics of weight loss and weight loss maintenance. In addition, we will present results from our recently published case control studies that examined EE and EI in successful weight loss maintainers compared to normal weight controls and controls with overweight/obesity. Based on these data and previous findings, we believe that high levels of PA may compensate for the reduction in TDEE that occurs during weight loss. The additional energy burned through PA raises PAEE (and thus TDEE) to a level at which the EI required to match TDEE is feasible for weight-reduced adults to maintain long-term. However, the only long-term studies to date that have evaluated intra-individual changes in EE and EI during weight loss maintenance had very small sample sizes (<15 subjects) and/or involved subjects that did not lose weight in a traditional way. We will provide an overview of the current literature regarding the relative contribution of EE and EI to weight loss and weight loss maintenance, highlight current literature gaps, and suggest directions for future research.