Walnut Ingestion in Adults at Risk for Diabetes: Effects on Body Composition, Diet Quality, and Cardiac Risk Measures

Inclusion Criteria: * Male and female age 25-75 years; * Non-smoker; * High risk for diabetes, defined as meeting at least one of the criteria listed below: a. Overweight with increased waist circumference; b.Pre-diabetes: fasting blood glucose \>100mg/dL and \<126mg/dL or HbA1C 5.7-6.4 % c. Metabolic syndrome, i.e. meet three out of five of the following criteria: i.Blood pressure \>130/85 mmHg or currently taking antihypertensive medication; ii. Fasting plasma glucose (FPG) \>100 mg/dL (6.1 mmol/L); iii.Serum triglycerides level (TG)\>150 mg/dL (1.69 mmol/L); iv. High-density lipoprotein (HDL) cholesterol \< 40 mg/dL (1.04 mmol/L) in men, and \< 50 mg/dL (1.29 mmol/L) in women; v. Overweight (BMI ≥25kg/m²) with waist circumference of more than 40 inches (102 cm) for men and more than 35 inches (88 cm) for women. Exclusion Criteria * Allergy to walnuts or any other nuts; * Anticipated inability to complete study protocol for any reason; * Current eating disorder; * Restricted diets by choice (i.e., vegetarian, vegan); * Receiving pharmacotherapy for obesity, including appetite suppressant * Unstable use of lipid-lowering, antihypertensive medications or aspirin (i.e. dose has changed in the three months prior to enrollment) or unwilling to refrain from taking medication for 12 hours prior to endothelial function scanning; * Regular use of high doses of vitamin E (\>400IU/day) or vitamin C (\>500mg/day); fish oil, flaxseed oil, omega-3 fatty acid and fiber supplement unless welling to discontinue supplementation for the study duration. * Use of insulin, glucose-sensitizing medication, vasoactive medication (including glucocorticoids, antineoplastic agents, psychoactive agents, or bronchodilators); * Diagnosed diabetes; * Diagnosed sleep apnea; * Established cardiovascular disease (including symptomatic coronary artery disease (CAD), myocardial infarction, peripheral vascular disease, congestive heart failure, carotid stenosis); * Coagulopathy, known bleeding diathesis, or history of clinically significant hemorrhage; current use of warfarin; * Regular exercise defined as participation in moderate-intensity exercise \> 150 minutes/week. * Substance abuse (chronic alcoholism, other chemical dependency) * Any unstable medical condition that would limit the ability of a subject to participate fully in the trial (e.g., cancer, AIDS, tuberculosis, psychotic disorder) * Women who get Depo-Provera shots * Women who are pregnant or lactating * Women who are currently on hormone replacement therapy * Substance abuse (chronic alcoholism, other chemical dependency) * Any unstable medical condition that would limit the ability of a subject to participate fully in the trial (e.g., cancer, AIDS, tuberculosis, psychotic disorder)