Twenty-one obese nondiabetic women (aged 23-53 years) were randomly assigned to consume for 16 weeks a low-calorie diet that was either 1) high in carbohydrate (60% of energy) and low in fat (20% of energy) (HC/LF) or 2) low in carbohydrate (40% of energy) and high in fat (40% of energy) (LC/HF). The women were classified as either insulin-sensitive (fasting insulin < 10 microU/ml; n = 12) or insulin-resistant (fasting insulin > 15 microU/ml; n = 9). Insulin-sensitive women on the HC/LF diet lost a mean of 13.5% of their initial body weight, whereas those on the LC/HF diet lost 6.8 % (p < 0.002 for the difference in the change between groups). In contrast, among insulin-resistant women, those on the LC/HF diet lost a mean of 13.4% of their initial body weight, whereas those on the HC/LF diet lost 8.5% (p < 0.04 for the difference in the change between groups). These differences could not be explained by changes in resting metabolic rate, activity, or food intake. Overall, changes in insulin sensitivity were associated with the degree of weight loss (r = -0.57; p < 0.05).

Comment: The results of this study suggest that the ideal weight-loss diet for an obese woman depends on her state of insulin sensitivity. Women who are insulin-sensitive lose weight more rapidly with a high-carbohydrate diet than with a low-carbohydrate diet. In contrast, a low-carbohydrate diet is more effective for women who are insulin-resistant. In both groups of women, weight loss resulted in improved insulin sensitivity. Diets high in complex carbohydrates, which contain abundant amounts of plant foods, are generally more healthful than low-carbohydrate diets, which usually contain more animal foods. Obese insulin-resistant women might fare best if they start on a low-carbohydrate diet and then switch to a high-complex-carbohydrate diet after their insulin sensitivity improves.

Cornier MA, et al. Insulin sensitivity determines the effectiveness of dietary macronutrient composition on weight loss in obese women. Obes Res 2005;13:703-709.