Low-Fat versus Low-Carbohydrate Weight Reduction Diets

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.  

A study was designed to investigate 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.  

The results of the study showed 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.  

From the results, the study demonstrated 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.

Published online in Diabetes before print August 31, 2009, doi: 10.2337/db09-0098