Effect of the intake of dietary protein on insulin resistance in subjects with obesity: a randomized controlled clinical trial

Purpose We compared the effect of diets with different amounts and sources of dietary protein on insulin sensitivity (IS) in subjects with obesity and insulin resistance (IR). Methods Eighty subjects with obesity (BMI >= 30 kg/m(2)) and IR (Matsuda index < 4.3 and HOMA-IR >= 2.5) over 18 years old were randomized to four groups for a one-month period: a normal protein diet (< 20%) with a predominance of animal protein (Animal NP) or vegetable protein (Vegetable NP) and a high-protein diet (25-30%) with a predominance of animal protein (Animal HP) or vegetable protein (Vegetable HP). Baseline and final measurements of body weight, body composition, biochemical parameters, blood pressure (BP), resting energy expenditure and plasma amino acid profiles were performed. Results Body weight, BMI and waist circumference decreased in all groups. Interestingly, the IS improved more in the Animal HP (Matsuda index; 1.39 vs 2.58, P = 0.003) and in the Vegetable HP groups (Matsuda index; 1.44 vs 3.14, P < 0.0001) after one month. The fat mass, triglyceride levels, C-reactive protein levels and the leptin/adiponectin index decreased; while, the skeletal muscle mass increased in the Animal and Vegetable HP groups. The BP decreased in all groups except the Animal NP group. Conclusion Our study demonstrates that a high-protein hypocaloric diets improves IS by 60-90% after one month in subjects with obesity and IR, regardless of weight loss and the source of protein, either animal or vegetable.