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

Proposed is a randomized, controlled, modified Latin square parallel design study with two treatment arms to examine walnut consumption effects on diet quality, body composition, and markers of cardiovascular risk in adults at risk for diabetes over a 6-month period. A modified crossover design (Latin square)27-29 will allow for both paired and unpaired analyses.

Specific Aims

* To determine the effects of a walnut-included diet (with or without caloric intake adjustment) versus walnut-excluded diet on diet quality in adults at risk for diabetes. Specifically, to show that a walnut-included diet, as compared to a walnut-excluded diet will improve overall diet quality as measured by the Alternative Healthy Eating Index in adults at risk for diabetes.
* To determine the effects of a walnut-included diet (with or without caloric intake adjustment) versus walnut-excluded diet on body composition in adults at risk for diabetes. Specifically, to show that a walnut-included diet, as compared to a walnut-excluded diet for 6 months will improve body fat percentage in adults at risk for diabetes.
* To assess the effects of a walnut-included diet (with or without caloric intake adjustment) for a 6-month period on endothelial function, lipid panel levels, fasting glucose level, fasting insulin level and anthropometric measures in adults at risk for diabetes. Specifically, to show clinically meaningful improvement in endothelial function, lipid panel, fasting blood glucose, hemoglobin A1c (HbA1c), anthropometric measures and endothelial function with inclusion of walnuts in the diet in adults at risk for diabetes.

Hypotheses

* A walnut-included diet with or without dietary counseling to adjust caloric intake will improve diet quality in adults at risk for diabetes.
* A walnut-included diet for 6 months with or without dietary counseling to adjust caloric intake will improve body composition in adults at risk for diabetes.
* A walnut-included diet with or without dietary counseling to adjust caloric intake will improve lipid panel, fasting blood glucose, hemoglobin A1c, endothelial function and anthropometric measures in adults at risk for diabetes.
* Controlling calorie intake to keep it constant with the addition of walnuts to the diet will enhance the beneficial effects of walnut ingestion on diet quality, body composition, and vascular function.

Eligibility Criteria:
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)