Effects of Intermittent Versus Continuous Energy Intakes on Insulin Sensitivity and Metabolic Risk in Women with Overweight

Objective: This study aimed to compare intermittent fasting (IF) versus continuous energy intakes at 100% or 70% of calculated energy requirements on insulin sensitivity, cardiometabolic risk, body weight, and composition. Methods: Women with overweight (n = 88; 50 ± 1 years, BMI 32.3 ± 0.5 kg/m²) were randomized to one of four diets (IF70, IF100, dietary restriction [DR70], or control) in a 2:2:2:1 ratio for 8 weeks. IF groups fasted for 24 hours after breakfast on three nonconsecutive days per week. All foods were provided and diets matched for macronutrient composition (35% fat, 15% protein, 50% carbohydrate). Insulin sensitivity by hyperinsulinemic-euglycemic clamp, weight, body composition, and plasma markers were assessed following a “fed” day (12-hour fast) and a 24-hour fast (IF only). Results: IF70 displayed greater reductions in weight, fat mass, total- and low-density lipoprotein cholesterol, and nonesterified fatty acids compared with DR70 and IF100 (all P ≤ 0.05). IF100 lost more weight and fat than control. However, fasting insulin was increased. There were no group differences in insulin sensitivity by clamp; however, a 24-hour fast transiently reduced insulin sensitivity. Conclusions: When prescribed at matched energy restriction, IF reduced weight and fat mass and improved total and low-density lipoprotein cholesterol more than DR. IF prescribed in energy balance did not improve health compared with other groups, despite modest weight loss.