This study is designed to determine the effects of dietary protein content on overfeeding.

When body weight increases, the expenditure of energy increases as a mechanism to dissipate the excess calories. The role of diet composition in over-feeding/energy dissipation in humans is unknown. We propose that:

1. High and low protein diet will result in less weight gain as compared to a moderate protein diet during a 56d high fat overfeeding.
2. Increase in energy expenditure and spontaneous physical activity, adjusted for lean and fat mass will be greater in the high and low protein diets as compared to a moderate protein diet.
3. the average size of the fat cells and the pattern of genes expressed in the adipose tissue, skeletal muscle, and peripheral blood mononuclear cells will "predict" which group of subjects will gain the most weight (and fat mass) independent of the level of the protein in the diet.

Inclusion Criteria:

• Have a BMI of 19-30kg/m2 A cutpoint of 26kg/m2 will be used to allocate treatment across the three diets. See the statistics section for more detail.
• Are willing to eat all of the study foods even when full
• Are willing to eat only foods provided by Pennington and all of the foods provided
• Are willing to live at Pennington for 10-12 weeks possibly without leaving the metabolic unit the entire time
• Are willing to avoid exercise while in the inpatient phase of the study
• Age 18 - 35

Exclusion Criteria:

Participants are ineligible to participate in the study if they…

• Smoke
• Have Diabetes
• Have claustrophobia
• Have a Fasting Blood Sugar >110
• Have a history of cardiovascular disease
• Have an average screening blood pressure >140/90
• Have a history of a major psychiatric, addictive or eating disorder or any psychosocial or scheduling factors that could impede study outcomes
• Post obese (self-reported BMI) must never have had a BMI greater than 32
• Exercise more than 2 hours per week
• Unable to complete VO2 max test.
• Weight gain or loss of > 3kg in the last 6 months
• Have significant renal, hepatic, endocrine, pulmonary or hematological disease, or a history of gout
• Have had previous GI surgery, Obstructive disease of the GI tract, Hypermotility disorder or a history of problems of impairment of the gag reflex.
• Corticosteroid use in the last 2 Months
• You are pregnant or breastfeeding
• Have Irregular menstrual cycles
• Use Depo-Provera, hormone implant or estrogen replacement therapy
• Have an allergy to PABA (a component of a B-vitamin often found in sunscreen)