Low Versus High-glycemic Index Post-exercise Diets for Improving Metabolism and Body Composition

Study Overview
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Brief Summary
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Postprandial triglycerides are a strong risk factor for heart disease. The purpose is to assess the effects of a low-glycemic versus high-glycemic meal after 90 minute exercise sessions that are done 4 times a week for 6 weeks on postprandial triglyceride level. Secondary measurements include other lipids and body composition.

Detailed Description
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The increase in triglycerides after a meal (i.e. postprandial triglycerides) is a strong risk factor for cardiovascular disease. Overweight/obese individuals have a greater triglyceride response to the same meal compared to lean individuals; therefore they are at greater risk. If exercise is performed the evening before a high-fat breakfast, the postprandial levels of triglycerides after the breakfast are reduced; however, if high glycemic index (GI) foods are consumed after the exercise session, the benefits of exercise on next-day postprandial triglycerides is negated. The investigators recently showed (HSFC funded) that consuming low GI foods after exercise is similar to fasting after exercise and superior to consumption of high GI foods for lowering next-day postprandial triglycerides. Low GI food was also superior for increasing fat oxidation, and lowering insulin, and low and very low density lipoproteins and preventing a decrease in high density lipoproteins. The benefits of an acute exercise session followed by low GI food consumption is now clear; however, it is not known whether this practice over weeks of exercise training results in accumulated and sustained benefits. The purpose of this study is to determine the chronic effects of consuming low compared to high GI foods after exercise sessions over six weeks in overweight and obese individuals. Twenty-four overweight and obese males and females will be randomized to consume either high or low GI foods immediately after exercise sessions (four sessions per week, 90 minutes per session, six weeks). At all other times of the day over the six weeks, they will be supplied a moderate GI diet, with calories and macronutrients based on four-day food diaries completed before the study. Two weeks before the intervention, participants will be required to go on the moderate GI diet, as a lead-in. One week into the lead-in, a baseline test will be done to determine postprandial metabolic responses (i.e. triglycerides, low and very low density lipoproteins, high density lipoproteins, insulin, and fat oxidation) after a morning high-fat breakfast. A week later, the same postprandial testing will be carried out the morning after the first exercise and post-exercise consumption of a low or high GI recovery meal. Participants will continue the training and post-exercise food consumption for the next six weeks, with postprandial measures taken again following the final exercise and feeding session. Body composition and aerobic fitness will be determined before and after the six week intervention. The investigators hypothesize that the low GI post-exercise feeding will be superior to the high GI post-exercise feeding for reducing body fat, improving fat oxidation, and reducing postprandial triglycerides, insulin and other harmful lipids. The results of the study will provide clinicians, exercise professionals and dietitians unique and experimentally tested strategies for their clients to lose body fat and improve metabolic profiles, to reduce the risk of heart disease.

Official Title
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Endurance Training and Post-exercise Low Glycemic Index Recovery Diet for Improving Postprandial Triglycerides

Conditions
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Hypercholesterolemia

Intervention / Treatment
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* Dietary Supplement: Low glycemic index post-exercise diet
* Dietary Supplement: High glycemic index post-exercise diet


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Overweight or obese (BMI 25 or greater) Exclusion Criteria: Smokers Diabetic Taking medications that affect carbohydrate or lipid metabolism

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 44 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: Parallel Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Low glycemic index post-exercise diet<br>Lentil-based post-exercise meal | Dietary Supplement: Low glycemic index post-exercise diet<br>* Feeding of a low-glycemic index, lentil meal after 90 minutes of walking exercise<br>|
| Active Comparator: High glycemic index post-exercise diet<br>Instant potato, white bread, and egg white post-exercise meal | Dietary Supplement: High glycemic index post-exercise diet<br>* Feeding of a high-glycemic index meal (i.e. instant mashed potatoes, white bread, egg whites) after 90 minutes of walking exercise<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Postprandial triglycerides | Triglyceride from serum | Change from baseline to 1 week and 6 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Postprandial cholesterol | Cholesterol from serum | Change from baseline to 1 week and 6 weeks | 
| Postprandial low density lipoprotein | Low density lipoprotein from serum | Change from baseline to 1 week and 6 weeks | 
| Postprandial high density lipoprotein | High density lipoprotein from serum | Change from baseline to 1 week and 6 weeks | 
| Postprandial glucose | Glucose from serum | Change from baseline to 1 week and 6 weeks | 
| Postprandial insulin | Insulin from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting Triglyceride | Triglyceride from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting cholesterol | Cholesterol from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting LDL-cholesterol | LDL from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting HDL-cholesterol | HDL from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting glucose | Glucose from serum | Change from baseline to 1 week and 6 weeks | 
| Fasting Insulin | Insulin from serum | Change from baseline to 1 week and 6 weeks | 
| Postprandial fat oxidation | Fat oxidation assessed by expiratory gases | Change from baseline to 1 week and 6 weeks | 
| Fat mass | Fat mass assessed by dual energy x-ray absorptiometry | Change from baseline to 6 weeks | 
| Waist Girth | Waist girth assessed by a measurement tape | Change from baseline to 6 weeks |