Background:
Dietary modification remains an essential component of successful weight loss strategies. No one dietary strategy has been determined to be superior to others for the general population. Studies that contrast reducing dietary fat vs. carbohydrate report consistently high within-group variability in dietary adherence and weight loss. Previous research by our group and others suggest that insulin-glucose dynamics or genotype patterns may modify diet effects.
Objective:
To determine if within-group weight loss variability on a Healthy Low-Fat (HLF) vs. a Healthy Low Carbohydrate (HLC) diet can be attributed to underlying factors such as insulin-glucose dynamics (i.e., insulin resistance and secretion) or genotype pattern. We hypothesized the above factors would be effect modifiers of HLF and HLC diets on 12-month weight loss.
Methods:
Generally healthy, non-diabetic adults, 18-50 years, BMI 28-40 kg/m
2
, were randomized to HLF or HLC with no specific prescribed energy restriction for 12 months (n=609). Health educators delivered the intervention in 22 1-hr group classes. Data were collected at 0, 3, 6, & 12 months. Dietary intake was assessed by three 24-hour recalls/time point. Clinical data includes: 75-g glucose oral glucose tolerance tests (insulin concentration at 30 minutes [Ins-30], a measure of insulin secretion), genotyping (3-SNP multilocus genotype: Low-Fat Genotype vs. Low-Carb Genotype, UK Biobank Axiom® array), body composition (DXA), resting energy expenditure (indirect calorimetry), epigenetics, proteomics, subcutaneous adipose tissue, microbiota, and standard CVD risk indicators.
Results:
At 12 months participants collectively lost 6,559 lbs. Retention was 79%, with equal dropout between arms. Range of weight change in both diet arms was ~80 lbs (-60 to +20 lbs). Macronutrient distribution at 12 months was 48% vs. 30% carbohydrate, 29% vs. 45% fat, and 21% vs. 23% protein for HLF and HLC, respectively. Both groups reported achieving and maintaining an average ~500 kcal deficit relative to baseline. Weight loss was similar for HLF vs. HLC: -12.1 ± 1.1 lbs vs. -13.8 ± 1.0 lbs, mean ± SEM. Neither Ins-30 (p for interaction = 0.84) nor genotype pattern (p for interaction = 0.20) modified the effect of diet on 12-month weight loss.
Conclusions:
Despite substantial weight loss, high within-group variability, and strong dietary differentiation between groups, neither baseline Ins-30 nor genotype pattern modified the effect of diet on 12-month weight loss. Focus on a healthy diet in both diet arms is novel in the context of many previous Low-Fat vs. Low-Carb studies and may have diminished expected effect modification. The extensive data set collected will be used to explore this and other potential explanatory factors.
Modeling the acute effects of exercise on glucose dynamics in healthy nondiabetic subjects
