Adolescents with severe obesity who underwent bariatric surgery experienced a 25% reduction in resting energy expenditure 12 months after the procedure, a figure greater than the level predicted by current BMI, suggesting careful nutritional management is warranted.
“It is known that weight loss reduces resting metabolic rate, or resting energy expenditure,” Jill Hamilton, MD, FRCPC, professor of pediatrics at the University of Toronto and director of the Centre for Healthy Active Kids at The Hospital for Sick Children in Toronto, told Endocrine Today. “In adolescents undergoing one of two common bariatric surgery procedures, Roux-en-Y gastric bypass and sleeve gastrectomy, we found that there was a reduction of approximately 550 kcal per day 1 year after surgery. Furthermore, this reduction was significantly lower than one would have predicted based on their current BMI by about 70 kcal per day. This is termed metabolic adaptation.”
Hamilton and colleagues analyzed data from 20 adolescents with obesity participating in the SickKids Team Obesity Management Program who underwent Roux-en-Y gastric bypass (n = 11) or sleeve gastrectomy between October 2010 and October 2017 (15 girls; mean age, 17 years; mean BMI, 48.7 kg/m²). Researchers used bioelectrical impedance analysis and indirect calorimetry to measure body composition and resting energy expenditure, respectively, and calculated predicted resting energy expenditure using the Mifflin equation before and after bariatric surgery.
At 1 year after surgery, resting energy expenditure decreased by a mean 548.3 kcal per day (P < .001). Metabolic adaptation, according to the researchers, was negative (mean, –103.7 kcal per day) and different from baseline (mean, 20.4 kcal per day; P = .043). Researchers observed no between-group differences when stratified by surgery type (P = .368).
Researchers found that a greater reduction in resting energy expenditure at 12 months was associated with a smaller total weight-loss percentage at 12 months (P < .001), a greater change in free fat mass at 12 months (P = .004) and a greater change in fat mass at 12 months (P < .001).
“The implications are that a teenager who loses a significant amount of weight will have to eat less than predicted for their current body weight if they are to maintain this weight,” Hamilton said. “This is one of the reasons that keeping weight off is so difficult. For example, if you were to continue to eat a total calorie intake at the ‘predicted’ resting energy expenditure, weight gain would occur at approximate a rate of 7 lb per year, based on the fact that 1 lb is approximately 3,500 kcal.”
The researchers noted that the underlying mechanisms contributing to metabolic adaptation are not well-understood. Potential mechanisms include decreased circulating leptin levels after surgery, decreased thyroid hormones linked to blunted sympathetic nervous system activity or decreased catecholamines associated with weight loss.
“Bariatric surgery is currently the most effective tool to improve metabolic complications of excess weight,” Hamilton said. “For long-term success in keeping this weight off, we need to find effective strategies to enhance metabolism and avoid metabolic adaptation.” – by Regina Schaffer
For more information:
Jill Hamilton, MD, FRCPC, can be reached at the Centre for Healthy Active Kids, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, M5G 1X8; email: firstname.lastname@example.org.
Disclosures: The authors report no relevant financial disclosures.