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.

Inclusion Criteria:

• Age: 18-70 years old.
• Body mass index between 27.5 - 40.
• Steady weight (± 4 kg) in the last 2 months.
• Glycated hemoglobin between 6 - 7%.

Exclusion Criteria:

• Anti-diabetic drugs (oral or subcutaneous) in the last 2 months.
• Lipid-lowering drugs in the last 2 months.
• Gouty arthritis in the last 2 years or uric acid > 735 mg/dl.
• Presence of uncontrolled endocrinological pathology (including hypothyroidism).
• Hepatic chronic disease (glomerular filtration rate < 45 ml/min).
• Renal, inflammatory or tumoral diseases.
• Drugs which could interfere in glucose or lipid metabolism such as androgens, corticosteroids (except for those with topic administration) and estrogen replacement therapy.
• Intake of functional foods with plant sterols in the past 6 weeks.
• High alcohol intake (> 30 g per day).
• Any serious disease which involves less than 1 year life expectancy or, in investigators judgment, limit the follow-up of an homogeneous diet throughout the study.
• Pregnancy or intention of pregnancy during the study.