1. No significant difference in weight change between a healthy low-fat diet and a healthy low-carbohydrate diet.
2. Genotype pattern or insulin secretion was not associated with dietary effects on weight loss
Evidence Rating Level: 1 (Excellent)
Study Rundown: Though the balance of macronutrients, such as carbohydrates and fats, have been thought to influence the success of weight loss strategies, there is great variability between those on a particular diet. While some have posited that genetic predisposition and insulin secretion patterns may explain this variability, these hypotheses have yet to be rigorously tested. In this randomized controlled trial, it was tested whether a set of 3 SNPs or baseline insulin secretion played a role in the success of a healthy low-fat (HLF) versus a healthy low-carbohydrate (HLC) diet to influence weight loss. The study found no differences in weight loss between the two diets, though both did result in improvements in body weight. In addition, neither the SNPs nor baseline insulin secretion influenced the rate or weight loss.
Overall, the rigorous design and appropriate number of subjects largely supports the conclusions that neither type of macronutrient, 3 SNP genotype, nor baseline insulin secretion greatly influences the ability of individuals to lose weight. As there still remained wide variability of subjects to lose weight within each group, this further suggests that the variables tested here are unlikely to impact a clinically meaningful amount of weight loss. While there are some limitations to this study, including poor generalizability across race or ethnicity and unknown impact of other genetic factors, this study strongly supports the conclusions that macronutrient make up is minimally important for success of weight loss.
Relevant Reading: The Merits of Subtyping Obesity: One Size Does Not Fit All
In-Depth [randomized controlled trial]: A total of 609 participants (mean age 40 years, 57% women, mean BMI 33, 79% completed study) were recruited from the Stanford and San Francisco Bay area and were randomized to HLC (30%), HLF (40%), or no intervention (30%). Some major criteria for exclusion included uncontrolled hypertension or metabolic disease, diabetes, cancer, heart, renal, or liver disease, or being pregnant or lactating. Intervention involved 22 instructional sessions over 12 months for both diet groups. Weight change at 12 months was -5.3 kg for HLF diet and -6.0 kg for HLC diet (difference 0.70, CI95 -0.21 to 1.60). No significant diet x genotype interaction (p = 0.20) or diet x insulin secretion interaction (p = 0.47) was found.
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