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

Study Overview
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Brief Summary
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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.

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

Conditions
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Diet Modification

Intervention / Treatment
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* Other: Low Glycemic Diet
* Other: High Glycemic Diet


Participation Criteria
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Eligibility Criteria
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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.

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 65 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Low Glycemic Diet<br> | Other: Low Glycemic Diet<br>* 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.<br>|
| Placebo Comparator: High Glycemic Diet<br> | Other: High Glycemic Diet<br>* 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.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Body composition | Body composition will be measured using Dual Energy X-Ray Absorptiometry (DXA) scan. | 10 months | 
| Resting energy expenditure | Resting energy expenditure will be measured by indirect calorimetry. | 10 months | 
| Total energy expenditure | Total energy expenditure will be measured by doubly labeled water. | 4 months | 
| Metabolic efficiency | Metabolic efficiency will be measured by submaximal exercise test. | 4 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Self-reported adherence of each diet | Self-reported adherence of each diet will be measured by interview. | 10 months |