Abstract

Objective: Low-fat hypocaloric diets reduce insulin resistance and prevent type 2 diabetes in those at risk. Low-carbohydrate high-fat diets are advocated as an alternative but reciprocal increases in dietary fat may have detrimental effects on insulin resistance and offset the benefits of weight reduction.

Research Design and Methods: We investigated a low-fat (20% fat, 60% carbohydrate) versus a low-carbohydrate (60% fat, 20% carbohydrate) weight reduction diet in 24 overweight/obese subjects, BMI 33.6±3.7 kg/m², age 39±10 years (mean ± SD), in an 8 week randomized controlled trial. All food was weighed and distributed and intake calculated to produce a 500kcal/day energy deficit. Insulin action was assessed by the euglycaemic clamp and insulin secretion by meal tolerance test. Body composition, adipokine levels and vascular compliance by pulse-wave analysis were also measured.

Results: Significant weight loss occurred in both groups (P<0.01), with no difference between groups (P=0.40). Peripheral glucose uptake increased but there was no difference between groups (P=0.28) and suppression of endogenous glucose production was also similar between groups. Meal tolerance-related insulin secretion decreased with weight loss with no difference between groups (P=0.71). The change in overall systemic arterial stiffness, was, however, significantly different between diets (P=0.04); this reflected a significant decrease in augmentation index following the low-fat diet, compared to a non-significant increase within the low-carbohydrate group.

Conclusions: This study demonstrates comparable effects on insulin resistance of low-fat and low-carbohydrate diets independent of macronutrient content. The difference in augmentation index may imply a negative effect of low-carbohydrate diets on vascular risk.