Effectiveness of energy-restricted diets with different protein:carbohydrate ratios: the relationship to insulin sensitivity.

Objective: Insulin sensitivity could determine the effectiveness of weight-loss diets with different protein:carbohydrate ratios. Our aim was to evaluate whether or not energy-restricted diets with different protein:carbohydrate ratios in obese individuals with (IR) or without (IS) insulin resistance could lead to differences in weight loss or insulin sensitivity.

Design: Prospective, randomized, clinical intervention study. Thirty-six obese patients, allocated to the IR or IS group after a 75 g oral glucose tolerance test and calculation of the homeostasis model assessment of insulin resistance (HOMA) index, were assigned to follow an energy-restricted diet with either 40 % carbohydrate/30 % protein/30 % fat (diet A) or 55 % carbohydrate/15 % protein/30 % fat (diet B) and followed up to 16 weeks.

Results: Twenty-one IR and fifteen IS patients were randomized to diet A or B. After 16 weeks, there was no difference in weight loss between diets A and B in each group. Glucose and insulin levels and HOMA were significantly reduced at 16 weeks, but no differences related to the type of diet were detected either in the IR or the IS group.

Conclusions: Varying the macronutrient composition of a hypoenergetic diet, regarding the percentage protein:carbohydrate ratio, did not produce different weight loss or result in an improvement in insulin sensitivity in people with or without insulin resistance.