Over the last four decades, obesity has become one of the major public health problems in the U.S. Due to its prevalence (>40% of the adult population are obese) there is an increased risk of comorbidities, especially Type 2 diabetes and cardiovascular disease.
Although weight loss is difficult, it is well established that weight loss interventions can be successful when participants are compliant. Diet, alone or in combination with exercise, can result in clinically relevant weight loss. However, maintenance of weight loss is much harder, with some patients relapsing to, or even above, baseline weight. Even though weight regain remains the main challenge in obesity management, the exact reasons for weight recidivism remain unexplained. The search for metabolic factors that may influence weight regain is, therefore, urgently needed.
Fat free mass (FFM) loss may play a role in influencing weight regain long term. It has been proposed that FFM can influence energy intake and body weight both directly and indirectly: directly through feedback signaling between FFM and brain centers involved in appetite control, and indirectly via its effects on resting energy expenditure and energy expenditure related to free-living activity. The Minnesota Starvation Experiment showed that larger FFM loss was associated with increased drive to eat during refeeding. However, this study included only lean men under near-starvation conditions.
Our study, published in Medicine & Science in Sport & Exercise® followed 141 premenopausal overweight women for one year following a 12 kg diet-induced weight loss. Subjects were randomly assigned to no training, aerobic training, or resistance training both during the weight loss and the one-year follow-up. Women who lost FFM during the weight loss phase regained 20% more weight in the following year, compared with women who did not lose FFM. As would be expected, FFM loss was larger after diet alone compared with diet plus aerobic training, while the diet-plus-resistance-training group did not lose FFM. What is particularly noteworthy is that the relationship between the percent FFM loss during weight loss and subsequent one-year weight regain was independent of the intervention used to induce weight loss. This strongly suggests that a greater FFM loss during dieting is a risk factor for more weight regain long term.
The exact mechanisms through which FFM loss increases the risk of weight regain are not clearly understood. The release of myokines from the muscle and potential interaction with brain centers involved in both homeostatic and hedonic appetite regulation, with an overall increase in the drive to eat, is a viable hypothesis. Alternatively, loss of FFM could reduce the ease of movement and decrease participation in physical activity.
Our results have important clinical implications, as they suggest that strategies to maintain, or even increase, muscle mass during weight loss by including resistance training should be strongly recommended to limit weight regain in the long term.
Catia Martins, PhD, has spent the last 10 years trying to understand the physiological mechanisms behind relapse in obesity management. She has also been interested on how exercise impacts the homeostatic appetite control system. She currently holds an associate professorship in the Department of Nutrition Sciences at the University of Alabama at Birmingham.
Gary R Hunter, PhD, is Distinguished Professor Emeritus in the Department of Nutrition Science at the University of Alabama at Birmingham. He has 40 years of experience in research designed to identify metabolic factors that predispose individuals to weight gain and strategies for enhancing free-living physical activity in older adults.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent ACSM positions or policies. Active Voice authors who have received financial or other considerations from a commercial entity associated with their topic must disclose such relationships at the time they accept an invitation to write for SMB.
