Low-carb diet ups energy expenditure during weight loss maintenance
A low-carbohydrate diet increases energy expenditure during weight loss maintenance, consistent with the carbohydrate-insulin model, a study has shown. This metabolic effect may contribute to the success of obesity treatment, particularly among those with high insulin secretion.
“Dietary composition seems to affect energy expenditure independently of body weight,” researchers said. “A low-glycaemic load, high-fat diet might facilitate weight loss maintenance beyond the conventional focus on restricting energy intake and encouraging physical activity.”
Intention-to-treat analysis in 162 participants showed that total energy expenditure varied by diet (p=0.002); for every 10-percent decrease in the contribution of carbohydrate to total energy intake (1 kcal, 4.18; kJ, 0.00418 MJ), there was a linear trend of 52 kcal/day (95 percent CI, 23–82). [BMJ 2018;363:k4583]
Change in total energy expenditure was greater in participants assigned to the moderate- (91 kcal/d; 95 percent CI, –29 to 210) and low-carbohydrate (209 kcal/d; 91–326) diets than in those assigned to the high-carbohydrate diet. Per protocol analysis in 120 participants (p<0.001) revealed differences of 131 kcal/d (–6 to 267) and 278 kcal/d (144–411), respectively.
The corresponding differences between low- and high-carbohydrate diet among participants in the highest third of preweight loss insulin secretion were 308 and 478 kcal/d in the intention-to-treat and per protocol analyses (p<0.004).
In both analyses, participants assigned to the low-carbohydrate diet had significantly lower ghrelin than those assigned to the high-carbohydrate diet. In per protocol analysis, participants assigned to the low-carbohydrate diet also had significantly lower leptin.
“Beyond effects on hunger, ghrelin has been reported to lower energy expenditure and promote fat deposition, providing another mechanistic explanation for our primary outcome,” researchers said. “Leptin, an adipocyte hormone that signals body energy stores, was also lower in participants assigned to the low carbohydrate diet, suggesting improvement in leptin sensitivity. [Curr Drug Targets 2005;6:153-169; Hormones (Athens) 2016;15:186-196; Obes Rev 2018;19:770-785]
In earlier prospective studies, findings showed that people with greatest reductions in leptin levels after weight loss had the lowest risk for weight regain. [J Clin Endocrinol Metab 2010;95:5037-5044; Int J Obes (Lond) 2011;35:785-792; Diabetes Obes Metab 2001;3:293-296]
The present randomized trial included 164 adults aged 18–65 years with a body mass index of ≥25 kg/m2. After 12 percent (within 2 percent) weight loss on a run-in diet, participants were randomized to one of three test diets according to carbohydrate content for 20 weeks: high, 60 percent, n=54; moderate, 40 percent, n=53; low, 20 percent, n=57.
Test diets were controlled for protein and were energy adjusted to maintain weight loss within 2 kg. Researchers divided that participants into thirds of preweight loss insulin secretion (insulin concentration 30 minutes after oral glucose) to test for effect modification predicted by the carbohydrate-insulin model.
“Additional research is warranted to examine the effects of glycaemic load on body weight, with control of energy intake; to compare diets aiming to reduce glycaemic index at prevailing carbohydrate levels (eg, the DIETFITS lower fat diet) compared with restricting total carbohydrate; to explore subgroup susceptibility based on insulin secretion and other biological factors; to determine whether extreme carbohydrate restriction (eg, with a ketogenic diet) confers unique advantages for obesity or specific conditions such as diabetes; and to explore the mechanisms relating dietary composition to energy expenditure,” researchers said.