A Study to Assess the Effect of a Normal vs. High Protein Diets in Carbohydrates Metabolism in Obese Subjects With Diabetes or Prediabetes

The objective of the study is to assess the effect of low-calorie diets with normal (18%) vs. high (35%) protein (mainly coming from animal source) composition on body weight and carbohydrates metabolism in overweight and obese subjects with pre-diabetes or diabetes. A dietary intervention is carried out during 6 months in 100 subjects who are individually randomized to an energy-restricted diet with two types of macronutrients composition: 1) 35% protein, 30% fat and 35% carbohydrates and 2) 18% protein, 30% fat and 52% carbohydrates. Around 80% of total protein in diet comes from animal source (of whom around 40% from lean red meat). Subjects are provided with weekly menus and different recipes to use them as part of the diet. Monitoring visits with the nutritionist will be performed every 15 days. At the beginning of the study, after 3 and 6 months, the following parameters are determined: anthropometric (weight, waist circumference, body mass index and body composition), blood pressure, dietary (72-hours dietary registry) and exercise and biochemical analysis (total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, apolipoproteins A1 and B, iron, transferring, ferritin, uric acid, glucose, HbA1c, insulin, adiponectin and resistin). Urine samples are also collected to assess microalbuminuria and ureic nitrogen.