Adults with obesity who have difficulty losing weight may have a biological variation that changes their energy expenditure response, according to research in Diabetes.
In a prolonged inpatient study of 12 men and women using a whole-room indirect calorimeter, researchers observed that participants who lost the least amount of weight during a 6-week, calorie-reduction period were those whose metabolism decreased the most during fasting – described by researchers as a “thrifty” metabolism.
“The degree of difficulty in weight loss varies, and this is a result of individual differences in biology,” Susanne Votruba, PhD, RD, clinical investigator with the Phoenix Epidemiology and Clinical Research Branch (PECRB) of the National Institute of Diabetes and Digestive and Kidney Diseases, told Endocrine Today. “Differences in metabolism were defined by the response to fasting. The fact that every volunteer in this study lost a significant amount of weight suggests that weight loss is plausible with sustained effort, regardless of biological differences.”
Votruba, Martin Reinhardt, MD, PECRB postdoctoral fellow, and colleagues analyzed data from 12 men and women with obesity in the PECRB facility’s metabolic unit. Participants spent an average of 77 days in the inpatient unit of the obesity and diabetes clinical research section, where they were limited to sedentary activity for the duration of the study.
Researchers took baseline measurements of the participants’ energy expenditure after a day of fasting using a whole-room indirect calorimeter, which calculates energy expenditure based on air samples. Participants then completed a 6-week phase of 50% calorie reduction. Researchers also performed bomb calorimetry of a duplicate weight-maintaining diet 3 days per week to accurately determine the participants’ energy intake and performed DXA scans biweekly. After the calorie-restriction period, participants maintained a standard 100% weight-maintaining diet based on their new weight for an average of 12 days.
In response to fasting and overfeeding, 24-hour energy expenditure decreased 9.4% (P < .001) and increased by 7.6% (P < .001), respectively. Participants with the smallest reduction in 24-hour energy expenditure lost the most weight in response to fasting (P < .001), described by researchers as a “thrifty” metabolism. Participants with the greatest 24-hour energy expenditure tended to lose the most weight with overfeeding (P = .22), described as a “spendthrift” metabolism. Results did not change after adjusting for age, sex, race and baseline weight.
“Clinically, it is difficult to determine which individuals are thrifty or spendthrift,” Votruba said. “However, as things currently stand, weight-loss strategies should be the same for everyone: Make smart food choices, practice portion control, and increase movement and exercise.
“That said, if a person knows – or suspects – that he or she has a thrifty metabolism, then he or she would need to be even more diligent,” Votruba said.
The researchers are seeking other indicators that can be more easily measured to identify people with varying metabolisms, Votruba said.
“We are also confirming our finding in larger groups of people, who are both obese and lean,” Votruba said. – by Regina Schaffer
The researchers report no relevant financial disclosures.