The findings represent the first study to examine whether metabolic adaptation, at the level of Resting Metabolic Rate (RMR), is associated with time to reach weight-loss goals.

The findings represent the first study to examine whether metabolic adaptation, at the level of Resting Metabolic Rate (RMR), is associated with time to reach weight-loss goals.New research from the University of Alabama at Birmingham Department of Nutrition Sciences is shedding light on why weight loss may take longer than expected, due to an exaggerated reduction in energy expenditure below predicted values (metabolic adaptation) in women with overweight.

The study, published in Obesity, The Obesity Society’s flagship journal, showed that premenopausal women with overweight experienced metabolic adaptation after a 16 percent weight loss, and those with the greater adaptation had to wait longer to see their weight loss goals come to fruition.

“Health care providers involved in obesity management, obesity researchers, individuals with obesity and the general public should pay close attention to these new findings,” said Catia Martins, PhD, associate professor in the UAB Department of Nutrition Sciences and lead author. “Delay in achieving weight-loss goals, or achieving a weight loss lower than expected, is generally seen as the direct and sole result of reduced adherence to the intervention.”

Martins explains this study shows that metabolic adaptation during weight loss is important in modulating weight-loss outcomes and likely to contribute to some of the inter-individual differences seen with weight-loss interventions. These findings represent the first study to examine whether metabolic adaptation, at the level of Resting Metabolic Rate (RMR), is associated with time to reach weight-loss goals.

A total of 65 White and Black premenopausal women ages 21 to 41 years old with overweight were selected for the study. The participants were sedentary (no more than one time per week of regular exercise) and had normal glucose levels, a family history of overweight/obesity in at least one first-degree relative, and no use of medications that affect body composition or metabolism. All participants were non-smokers and reported a regular menstrual cycle.

Participants included in the retrospective analysis came from two different studies — ROMEO and JULIET performed in the UAB Department of Nutrition Sciences with the same sequence of events and methodologies and both aiming to identify metabolic predictors of weight regain. In the ROMEO study, all participants achieved weight loss with diet alone, while in the JULIET study, participants were randomly assigned to one of three groups: weight loss with aerobic exercise training three times a week, weight loss with resistance exercise training three times a week and weight loss with diet alone (same diet as in ROMEO).

For the present study, researchers included all participants from the ROMEO study and the participants randomized to diet only from the JULIET study. All participants were provided an 800-kcal diet until reaching a BMI of greater than or equal to 25 kg/m2. After a four-week weight-stabilization period at baseline and after weight loss, testing was conducted in the follicular phase of the participants’ menstrual cycle in a fasted-state during a four-day, in-patient stay.

Martins says the most important determinant of success in dietary interventions is undoubtedly diet adherence; however, metabolic adaptation also plays a significant role.

“It needs to be acknowledged that the larger the weight loss, the larger the metabolic adaptation, so is not unexpected that weight loss gets harder over time, and the last pounds might be really hard to lose,” Martins said. “However, metabolic adaptation is not a permanent adaptation. It is significantly reduced or even disappears after a short period of weight stabilization, let’s say a couple of weeks. So, for those who struggle to lose the last pounds, despite adherence to the energy-restricted diet, there is good news. If they stabilize their weight for a couple of weeks, metabolic adaptation will be reduced or even go away, and then they can try again to lose weight and have a better chance to succeed.”

Other authors of the study include Barbara Gower, PhD, professor and vice chair for Research, and Gary Hunter, PhD, professor emeritus, in the UAB Department of Nutrition Sciences.

This work was supported by National Institutes of Health grants R01 DK049779, P30 DK56336, P60 DK079626 and UL 1RR025777.