Effects of Low Fat Versus Low Carbohydrate Diets on Energy Metabolism

Competing theories about obesity and its treatment contrast the relative roles of dietary fat versus carbohydrate on promotion of excessive calorie intake. Advocates of low-carbohydrate diets propose that diets high in carbohydrates lead to elevated insulin secretion and increased calorie intake. Alternatively, proponents of low-fat diets argue that diets high in fat promote passive overconsumption due to the high energy density and low satiety index of high-fat foods. Therefore, we will conduct a feeding study in 20 adult men and women to investigate the differences in ad libitum energy intake resulting from consuming two test diets for a pair of 2-week periods in a randomized, crossover design during a single 4-week inpatient period. The test diets presented to participants will be matched for calories and protein, but the low-carbohydrate diet (approximately10% of calories) will be high in fat (approximately75% of calories) whereas the low-fat diet will be high in carbohydrates (approximately75% of calories) and low in fat (approximately 10% of calories).

• INCLUSION CRITERIA:

• Adults age 18-50 years, male and female
• Weight stable (less than or equal to 5 % over past 6 months) as determined by volunteer report
• Body mass index (BMI) greater that or equal to 20kg/m2
• Body weight greater than or equal to 53 kg
• Able to complete daily bouts of stationary cycling at a moderate rate and intensity with a heart rate (HR) equal to or greater than 0.3(SqrRoot) (220-age-HRrest)+HRrest but not exceeding 0.4(SqrRoot) (220-age-HRrest)+HRrest and no signs of arrhythmia

Exclusion criteria

• Evidence of metabolic or cardiovascular disease, or disease that may influence metabolism (e.g. cancer, diabetes, thyroid disease)
• Taking any prescription medication or other drug that may influence metabolism (e.g. diet/weight-loss medication, asthma medication, blood pressure medication, psychiatric medications, corticosteroids, or other medications at the discretion of the PI and/or study team)
• Positive pregnancy test or lactation as determined by volunteer report (women only)
• Participating in a regular exercise program (> 2h/week of vigorous activity) as determined by volunteer report
• Hematocrit <37% (women only)
• Hematocrit < 40% (men only)
• Caffeine consumption > 300 mg/day as determined by volunteer report
• Regular use of alcohol (> 2 drinks per day), tobacco (smoking or chewing) amphetamines, cocaine, heroin, or marijuana over past 6 months as determined by volunteer report
• Psychological conditions such as (but not limited to) eating disorders, claustrophobia, clinical depression, bipolar disorders, that would be incompatible with safe and successful participation in this study, as determined by investigators.

• Past or present history of eating disorders as determined by volunteer report
• Past or present history of claustrophobia since part of the protocol will involve being confined to a small room for whole-body indirect calorimetry and being in an MRI scanner for liver fat measures
• Implants, devices, or foreign objects implanted in the body that interfere with the Magnetic Resonance procedures
• Volunteers with strict dietary concerns (e.g. vegetarian or kosher diet, food allergies)
• Volunteers unwilling or unable to give informed consent
• Non-English speakers due to unavailability of required questionnaires in other languages