Hypothesis: Chronic intake of pistachios improves glucose metabolism and insulin resistance status thus contributing to decrease the risk of type 2 diabetes mellitus and its associated abnormalities.

In free-living overweight or obese adult with impaired fasting glucose or impaired glucose tolerance we will compare the effects of a pistachio-rich diet or a Mediterranean Diet on:

• Fasting glucose levels, hemoglobin A1c, insulin, C peptide, HOMA IR, advanced glycation end products and soluble receptor of advanced glycation-end products.
• Peripheral haemostatic parameters.
• Plasma inflammatory markers.
• Lymphocyte expression of toll-like receptors, C peptide, resistin and interleukin-6 in peripheral leukocytes.
• Lymphocyte glucose transport and expression of glucose transporter 4 in peripheral blood leukocytes.
• Platelet function including platelet number, mean platelet volume, platelet factor 4 levels and urinary 11-dehydro-thromboxane B2.

Inclusion Criteria:

• BMI less than 35 kg/m2.
• Fasting plasma glucose levels between 100 and 125 mg/dl or
• Oral glucose tolerance test of 140 to 199 mg/dl.

Exclusion Criteria:

• Diabetes mellitus.
• Alcohol, tobacco, or drug abuse.
• Significant liver, kidney, thyroid, or other endocrine diseases.
• Frequent consumption of nuts or known history of allergy to them.
• Use of plant sterol, oral antidiabetic drugs, supplemental use of phyllium, fish oil supplements and multivitamins, vitamin E or other antioxidant supplements.
• Bad dentures, implying difficulty to chew pistachios.
• Being pregnant or wishing to become a pregnant 6 months before or during the study, lactating 6wk before or during the study.
• Following vegetarian or weight loss diets.
• Other medical or social conditions that difficult the compliance to the intervention.