Metabolic adaptation to weight loss may be overestimated

WASHINGTON — Adults who lose a considerable amount of body weight may not experience a decline in metabolic rate that makes it difficult to maintain weight loss as suggested by some recent studies, according to study findings presented here.

“A substantial degree of metabolic adaptation in [resting energy expenditure] may not be a universal part of the biologic pressure to regain weight for all individuals maintaining weight loss,” said presenter Danielle M. Ostendorf, a doctoral candidate at the Colorado School of Public Health in Aurora.

Ostendorf and colleagues found that some equations developed to predict resting energy expenditure — specifically, the equation developed from “The Biggest Loser” data by Kevin D. Hall, PhD, and colleagues from National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health — may overestimate the amount of energy needed to maintain body weight in certain patients, implying that the perceived discrepancy in expected vs. actual metabolic rate is inaccurate.

In a post hoc analysis of data collected as part of a case-control study from October 2009 to August 2012, the researchers calculated actual and predicted resting energy expenditure for adults aged 18 to 65 years with stable weight in three groups: 34 weight-loss maintainers who kept off losses of at least 13.6 kg for at least 1 year, 35 normal-weight controls, and 33 controls with overweight or obesity who were matched to the pre-weight-loss BMI of the weight-loss maintainers.

Resting energy expenditure was measured through indirect calorimetry for each participant twice over 7 days. The researchers used three different methods for determining predicted resting energy expenditure for the participants: first, using the actual resting energy expenditure, age, sex, fat mass and fat-free mass, they developed a best-fit linear regression model; second, they applied three validated predictive equations (Harris and Benedict equation, Mifflin equation and an equation based on organ mass); and, third, they used the predictive equation developed in the study of “The Biggest Loser” contestants. They then compared actual and predicted resting energy expenditure values in paired-samples t-tests.

The researchers found that, among the entire cohort, the first two methods of predicting resting energy expenditure among the weight loss maintainers were relatively accurate whereas the third method significantly overestimated the value by 16% to 26%.

However, the researchers noted large variability between individuals. “Those who have a higher maximum weight or higher maximum BMI are more likely to exhibit a lower than predicted resting energy expenditure,” Ostendorf said. “Also, those who have a higher weight loss are more likely to exhibit a lower than predicted resting energy expenditure.”

Length of weight loss maintenance was not correlated with resting energy expenditure, according to Ostendorf.

“Somebody who may be wondering why our results differ from The Biggest Loser study ... we found a 13.9 kcal difference per day whereas The Biggest Loser [researchers] found a difference of 449 kcal per day,” Ostendorf said.

These discrepancies can likely be attributed to different study designs and the much greater and more rapid weight loss experienced by The Biggest Loser contestants, she said. — by Jill Rollet

Reference:

Fothergill E, et al. Obesity. 2016;doi:10.1002/oby.21538

Ostendorf DM. T-OR-LB-2079. Presented at: ObesityWeek 2017; Oct. 29-Nov. 2, 2017; Washington, D.C.

Disclosure: Ostendorf reports no relevant financial disclosures.