Obesity Risk in African American Women is Determined by a Diet-by-phenotype Interaction

The Scientific Premise of this study is that the high level of obesity displayed by African American (AA) women is due to the ability to secrete large amounts of insulin when sugary foods are consumed. When AA women eat a diet rich in starchy or sugary food (a "high-glycemic" diet that stimulates insulin secretion), the food that is eaten is stored as fat rather than being burned as fuel. The investigators previous research has suggested that AA women have an easier time losing weight and keeping it off when eating a low-glycemic diet. The proposed study will be the first randomized clinical trial to test the effect of high and low glycemic diets for weight loss and weight-loss-maintenance in obese AA women.

Low Glycemic (LG) diet: The LG diet will be made up of foods that do not stimulate insulin secretion. The foods that make up the diet will differ depending on the phase of the study. During the weight loss phase, breakfast and lunch will each consist of one or two meal-replacement "shakes" (e.g., High-Protein SlimFast). Dinner will be a frozen entrée (e.g., Atkins, Lean Cuisine, Healthy Choice) supplemented with a side of vegetables. Snacks will be nuts, berries, and full-fat dairy products (one serving per day), and will be used to adjust the calorie level of each day's meals to individual calorie needs.

High Glycemic (HG) diet: The HG diet will conform to United States Department of Agriculture (USDA) guidelines (http://health.gov/dietaryguidelines/2015/guidelines/). The foods that make up the diet will differ depending on the phase of the study. During the weight loss phase, breakfast and lunch will each consist of one or two meal-replacement "shakes" (e.g., SlimFast). Dinner will be a frozen entrée (e.g., Lean Cuisine, Healthy Choice) supplemented with a side of vegetables. Snacks will be fruit, fat-free dairy products, and low-fat bars (e.g., Optifast), and will be used to adjust the calorie level of each day's meals to individual calorie needs.

Inclusion Criteria: BMI 30-45 kg/m2 Sedentary to moderately active (<2 hours/wk of moderate, structured, intentional exercise. Normal menstrual cycle Exclusion Criteria: History of eating disorder daily use of tobacco (>1 pack/wk) change in weight greater than 5 pounds in previous 3 months presence of any condition (e.g. PCOS) or use of any medication (e.g. glucocorticoid) deemed by the project physician to interfere with study outcomes applicants will be screened with a standard oral glucose tolerance test. If a participant's 2 hour glucose if >200, they will not be able to enroll in the study.