Objective: To compare the effects of two calorie-restricted diets that differ in glycemic load (GL) on glucose tolerance and inflammation.
Research methods and procedures: Thirty-four healthy overweight adults, ages 24 to 42 years, were randomized to 30% provided calorie-restricted diets with high (HG) or low (LG) glycemic load for 6 months. Outcomes were changes in glucose-insulin dynamics and C-reactive protein (CRP) levels.
Results: Compared with baseline, levels of fasting insulin, homeostasis model assessment of insulin resistance, post-load insulin at 30 minutes, and incremental area-under-the-curve-insulin during the oral glucose tolerance test were significantly lower in both groups at 6 months (p range, 0.01 to 0.05), but after adjustment for baseline values and weight change, there were no differences between the two groups with regard to changes over time in any parameter. The mean percentage change in insulin sensitivity by a frequently sampled intravenous glucose tolerance test was +26% in the HG group and +24% in the LG group (p = 0.83); first-phase acute insulin release was -20% in the HG group and -21% in the LG group (p = 0.77). More participants on the LG diet (14 of 16 subjects) had a decline in serum CRP, compared with those on the HG diet (7 of 16 subjects) (p < 0.05).
Discussion: In healthy overweight adults provided with food for 6 months, the dietary GL did not seem to influence chronic adaptations in glucose-insulin dynamics above that associated with weight loss. This finding highlights the importance of absolute weight loss over the dietary macronutrient composition used to achieve weight loss. The finding of greater declines in CRP concentration after consumption of a low-GL diet warrants further investigation.