Popular Diets Study

Study Overview
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Brief Summary
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The aim of this study is to evaluate the effects of three dominant dietary patterns - conventional low-fat, low-glycemic index (GI) and very-low-carbohydrate - on energy metabolism and heart disease risk factors following weight loss in obese young adults in a feeding study

Detailed Description
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For most of the last half century, reduction in fat intake has been the primary nutritional approach for the prevention and treatment of obesity and cardiovascular disease (CVD). Over the last few years, very low carbohydrate (Atkins-type) diets have achieved great popularity, with publication of several studies suggesting greater weight loss and improvements in CVD risk factors over 3 to 6 months. Recently, a third dietary approach focused on glycemic index (GI) has generated interest. However, few studies have compared the effects of these diets on body weight regulation and risk for CVD. The primary hypotheses of this study are that any diet that lowers the postprandial rise in blood glucose (very-low-carbohydrate or low-GI) will have beneficial effects on the physiological adaptations to weight loss and on some CVD risk factors. However, other CVD risk factors will be adversely affected by a very-low-carbohydrate vs. a low-GI diet. Preliminary data provide strong support for these hypotheses, by showing that resting energy expenditure declines less and CVD risk factors improve more with weight loss on a low-glycemic load diet compared to a conventional low-fat diet. This application proposes a cross-over feeding design to study the effects of three diets following 12.5% weight loss in obese young adult subjects (n = 24, age 18 to 40 years). The diets are: 1) conventional low-fat, with 60% carb, 20% fat, 20% protein; 2) low-GI with 40% carb, 40% fat, 20% protein; and 3) very-low-carbohydrate with 10% carb, 60% fat, 30% protein. The primary outcome is resting energy expenditure (indirect calorimetry). Secondary outcomes include total energy expenditure (doubly labeled water), thermic effect of food (indirect calorimetry), physical activity (accelerometry), insulin resistance and B-cell function (frequently-sampled OGTT), blood lipids, blood pressure and measures of systemic inflammation and coagulopathy. This study should have major public health implications to the millions of Americans currently following diets to decrease body weight and risk for heart disease.

Official Title
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Popular Diets, Metabolism, and CVD Risk

Conditions
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Obesity, Insulin Resistance

Intervention / Treatment
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* Other: Low glycemic index diet
* Other: Low fat diet
* Other: Very low carbohydrate diet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: BMI ≥ 27 kg/m2 Willing and able to come to the GCRC 5 days per week to consume a supervised meal and pick-up food for all other meals Available for scheduled hospital admissions Willing to abstain from alcohol consumption for the duration of the study If female, regular menstrual cycles (defined as 26 to 30 days between cycles; no more than one day variation in the duration of menstrual flow) Exclusion Criteria: Weight > 350 lbs Change in body weight (± 10%) over preceding year Taking any medications or dietary supplements that might affect body weight, appetite, or energy expenditure Smoking (1 cigarette in the last week) High levels of physical activity Currently following a special diet Abnormal laboratory screening tests Type 2 diabetes mellitus Allergies or aversions to foods on the study menu Previous diagnosis of an eating disorder or any other mental health disorder If female, pregnant in the past 12 months or planning to become pregnant during the study period If female, lactating in the preceding 12 months If taking birth control medication, change in medication in previous 3 months or plans to change medication during the study period

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

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: Prevention
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: 1<br>Low glycemic index diet | Other: Low glycemic index diet<br>* Feeding protocol, all foods prepared in a metabolic kitchen<br>|
| Active Comparator: 2<br>Low fat diet | Other: Low fat diet<br>* Feeding protocol, all foods prepared in a metabolic kitchen<br>|
| Active Comparator: 3<br>Very low carbohydrate diet | Other: Very low carbohydrate diet<br>* Feeding protocol, all foods prepared in a metabolic kitchen<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| resting energy expenditure using indirect calorimetry in the fasting state |  | end of each dietary period | 
| insulin resistance assessed by frequently-sampled oral glucose tolerance test |  | end of each dietary period | 
| thyroid function tests |  | end of each dietary period | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| total energy expenditure using doubly labeled water methodology |  | end of each dietary period | 
| thermic effect of food using indirect calorimetry |  | end of each dietary period | 
| physical activity using accelerometry |  | end of each dietary period | 
| serum lipids |  | end of each dietary period | 
| plasminogen activator inhibitor-1 |  | end of each dietary period | 
| C-reactive protein |  | end of each dietary period | 
| blood pressure |  | end of each dietary period | 
| hunger/appetite |  | end of each dietary period | 
| insulin 30 minutes after oral glucose (as an effect modifier) |  | baseline | 
| Core temperature |  | End of each dietary period | 
| secreted frizzle-related protein-4 |  | end of each dietary period | 
| heme-oxygenase |  | end of each dietary period | 
| Irisin |  | end of each dietary period | 
| fibroblast growth factor-21 |  | end of each dietary period | 
| chemerin |  | end of each dietary period | 
| trimethylamine N-oxide |  | fasting and postprandial, end of each dietary period | 
| alanine aminotransferase |  | end of each dietary period | 
| Uric acid |  | end of each dietary period | 
| insulin |  | fasting and postprandial, end of each dietary period | 
| ghrelin |  | fasting and postprandial, end of each dietary period | 
| gastric inhibitory peptide |  | fasting and postprandial, end of each dietary period | 
| GLP1 |  | fasting and postprandial, end of each dietary period | 
| PYY |  | fasting and postprandial, end of each dietary period | 
| Amylin |  | fasting and postprandial, end of each dietary period | 
| Leptin |  | end of each dietary period | 
| Metabolomic analysis | Evaluate the effect of diet on metabolomic profile in plasma, with the aim of assessing dietary adherence and exploring diet-disease mechanisms | end of each dietary period | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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obesity, nutrition