The purpose of this study is to compare a diet containing whole grains versus an energy matched diet using refined grains on body composition and metabolism.

The investigators hypothesis is that a diet high in whole-grains reduces abdominal fat. These findings might have clinical and public health significance for reducing obesity and related co-morbidities like type 2 diabetes and cardiovascular disease. Using a double-blind cross-over design, energy expenditure, body composition and metabolic health will be assessed. Three day inpatient study visits to the Cleveland Clinic Clinical Research Unit (CRU) will be implemented for metabolic control and testing. Total daily energy expenditure will be measured using the doubly labeled water (DLW) method. Body fat and glucose/protein metabolism will be assessed by imaging and isotope techniques, respectively. Blood, urine, and stool samples will also be collected for cardiometabolic and digestive health outcomes. After baseline testing, subjects will begin an 8 week dietary intervention, where all food and non-water beverages will be supplied by the study center. Dietary compliance will be assessed by weigh back measurements two times a week. To assess time course effects of diets differing in the amount of fiber on body composition and metabolic health, subjects will provide plasma and urine samples 2, 4, and 8 weeks after initial testing. Imaging and isotope analysis will be performed baseline and at week 8. All post testing will be conducted after week 8 following similar pre-testing control conditions. Subjects will then undergo an 8-10 week washout period where they will be instructed to return to their normal diet (except for any supplements). After the washout period, subjects will start the second arm of the intervention and consume the alternate diet (i.e. refined or whole grain diet). All energy expenditure, body composition and metabolic testing procedures will be repeated during the alternative arm of the study as described above.

Inclusion Criteria:

• Aged between 20-50 years
• BMI between 25 and 38 kg/m2
• Normal whole grain intake <1 serving/d (Appendix 1)
• Low average consumption of alcohol (<1 standard drink/day; <7 standard drinks/week)
• Non-smoker
• No major chronic illness
• Fasting glucose <126 mg/dl
• Able to access the study centre (Lerner Research Institute and the Clinical Research Unit at the Cleveland Clinic) throughout the study
• Have access to a microwave oven and refrigerator/freezer

Exclusion Criteria:

• Any known food allergy with the possibility to result in a serious adverse reaction, or an allergy to a food item that cannot be removed from the diet (i.e. peanuts).
• Aversion or dislike to study foods
• Regular use of dietary supplements and not willing/able to stop usage during the study period
• Cardiovascular conditions including significant known coronary artery disease, arrhythmia, known peripheral vascular disease (large vessel disease), uncompensated congestive heart failure, history of stroke, or uncontrolled hypertension (defined as medically treated with the mean of 3 separate measurements SBP > 180 mm Hg or DBP > 110 mm Hg)
• Severe pulmonary disease defined as FEV1 < 50% of predicted value
• Kidney disease including diagnosed chronic kidney disease, renovascular hypertension, renal artery stenosis, or chronic renal insufficiency with a creatinine level > 1.8 mg/dl
• Known history of chronic liver disease (except for NAFLD), hepatitis, positive serologic test result for hepatitis B surface antigen and/or hepatitis C antibody, α-1-antitrypsin deficiency
• GI disorders including a known history of celiac disease and/or any other malabsorptive disorders or inflammatory bowel disease (Crohn's disease or ulcerative colitis)
• Psychiatric disorders including dementia, active psychosis, severe depression (requiring > 2 medications), history of suicide attempts, alcohol or drug abuse within the previous 12 months
• Other known metabolic disease such as clinical hypothyroidism and hyper thyroidism, Graves Disease, thyroid cancer, nodules or multinodular goiter
• Malignancy within five years (except squamous cell and basal cell cancer of the skin)