Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial.
Study Goal
The researchers aimed to determine the effects of varying carbohydrate-to-fat ratio diets on total energy expenditure during weight loss maintenance, particularly testing the carbohydrate-insulin model.
Results Summary
The study found that lowering dietary carbohydrate intake increased total energy expenditure, with the low-carbohydrate diet showing the greatest effect (209 kcal/d higher than the high-carbohydrate diet). The effect was more pronounced in participants with high pre-weight loss insulin secretion (308 kcal/d difference). Ghrelin and leptin levels were also significantly lower in the low-carbohydrate group.
Population
164 adults aged 18-65 with a BMI ≥ 25, who achieved a 12% weight loss prior to the intervention.
Effective Dosage
Diets with 20% (low), 40% (moderate), or 60% (high) carbohydrate content, adjusted to maintain weight loss within 2 kg.
Duration
20 weeks
Interactions
None mentioned
| Intervention | Direction | Endpoint | Population | Dosage | Impact | Claim # |
|---|---|---|---|---|---|---|
low carbohydrate diet (20%) | increase | total energy expenditure | adults aged 18-65 years with a body mass index of 25 or more | 209 kcal/d greater compared with the high carbohydrate diet | increased | #1 |
moderate carbohydrate diet (40%) | increase | total energy expenditure | adults aged 18-65 years with a body mass index of 25 or more | 91 kcal/d greater compared with the high carbohydrate diet | increased | #2 |
decrease in the contribution of carbohydrate to total energy intake | increase | total energy expenditure | adults aged 18-65 years with a body mass index of 25 or more | 52 kcal/d for every 10% decrease | linear trend of increase | #3 |
low carbohydrate diet (20%) | decrease | ghrelin levels | adults aged 18-65 years with a body mass index of 25 or more | - | significantly lower | #4 |
low carbohydrate diet (20%) | decrease | leptin levels | adults aged 18-65 years with a body mass index of 25 or more | - | significantly lower | #5 |
low carbohydrate diet (20%) | increase | total energy expenditure | participants in the highest third of pre-weight loss insulin secretion | 308 kcal/d greater compared with the high carbohydrate diet (intention-to-treat) | increased | #6 |
low carbohydrate diet (20%) | increase | total energy expenditure | participants in the highest third of pre-weight loss insulin secretion | 478 kcal/d greater compared with the high carbohydrate diet (per protocol) | increased | #7 |
OBJECTIVE: To determine the effects of diets varying in carbohydrate to fat ratio on total energy expenditure. DESIGN: Randomized trial. SETTING: Multicenter collaboration at US two sites, August 2014 to May 2017. PARTICIPANTS: 164 adults aged 18-65 years with a body mass index of 25 or more. INTERVENTIONS: After 12% (within 2%) weight loss on a run-in diet, participants were randomly assigned to one of three test diets according to carbohydrate content (high, 60%, n=54; moderate, 40%, n=53; or low, 20%, n=57) for 20 weeks. Test diets were controlled for protein and were energy adjusted to maintain weight loss within 2 kg. To test for effect modification predicted by the carbohydrate-insulin model, the sample was divided into thirds of pre-weight loss insulin secretion (insulin concentration 30 minutes after oral glucose). MAIN OUTCOME MEASURES: The primary outcome was total energy expenditure, measured with doubly labeled water, by intention-to-treat analysis. Per protocol analysis included participants who maintained target weight loss, potentially providing a more precise effect estimate. Secondary outcomes were resting energy expenditure, measures of physical activity, and levels of the metabolic hormones leptin and ghrelin. RESULTS: Total energy expenditure differed by diet in the intention-to-treat analysis (n=162, P=0.002), with a linear trend of 52 kcal/d (95% confidence interval 23 to 82) for every 10% decrease in the contribution of carbohydrate to total energy intake (1 kcal=4.18 kJ=0.00418 MJ). Change in total energy expenditure was 91 kcal/d (95% confidence interval -29 to 210) greater in participants assigned to the moderate carbohydrate diet and 209 kcal/d (91 to 326) greater in those assigned to the low carbohydrate diet compared with the high carbohydrate diet. In the per protocol analysis (n=120, P<0.001), the respective differences were 131 kcal/d (-6 to 267) and 278 kcal/d (144 to 411). Among participants in the highest third of pre-weight loss insulin secretion, the difference between the low and high carbohydrate diet was 308 kcal/d in the intention-to-treat analysis and 478 kcal/d in the per protocol analysis (P<0.004). Ghrelin was significantly lower in participants assigned to the low carbohydrate diet compared with those assigned to the high carbohydrate diet (both analyses). Leptin was also significantly lower in participants assigned to the low carbohydrate diet (per protocol). CONCLUSIONS: Consistent with the carbohydrate-insulin model, lowering dietary carbohydrate increased energy expenditure during weight loss maintenance. This metabolic effect may improve the success of obesity treatment, especially among those with high insulin secretion. TRIAL REGISTRATION: ClinicalTrials.gov NCT02068885.