The purpose of this trial is to examine the metabolic and behavioral effects of a positive energy balance induced by adding food to the usual level of activity.

It is hypothesized that: 1) food intake will not differ significantly after 2 days of positive energy balance induced by a high carbohydrate vs. high fat diet when both diets are low in energy density, and 2) food intake will be higher after a positive energy balance induced by a high fat/high energy dense diet vs. a high fat/low energy dense diet.

The purpose of this trial is to examine the metabolic and behavioral effects of a positive energy balance induced by adding food to the usual level of activity. During this study, we will induce a positive energy balance for two days by increasing food intake to 140% of baseline energy requirements and keeping energy expenditure constant. The following three diets, which vary in dietary fat and energy density (kcal/g), will be used to induce the positive energy balance in a within subjects or cross over design: 1) high fat/high energy density, 2) high fat/low energy density, and 3) high carbohydrate/low energy density. Food intake and activity will be measured for 4 days after each diet to quantify the response to positive energy balance and manipulation of dietary fat and energy density.

Inclusion Criteria:

• You are between the ages of 18 and 50, inclusive, if you are a male or between the ages of 18 and 45, inclusive, if you are a female.
• Your body mass index (BMI) is between 20 and 40 kg/m², inclusive.
• For females, if you have regular menstrual periods, with no less than 28 day cycles. Monophasic birth control pills, copper IUD, Ortho Evra patch, NuvaRing or complete hysterectomy are also acceptable.

Exclusion Criteria:

• You have a chronic disease that affects body weight, appetite, or metabolism, such as diabetes and cardiovascular disease.
• You have irregular menstrual cycles, had a partial hysterectomy (still maintain ovaries), or use an IUD not made of copper.
• You use prescriptions or over-the-counter medications or herbal products that affect metabolism or body weight (e.g. weight loss medications such as sibutramine, or orlistat).
• You use a birth control pill that isn't monophasic or you receive Depro-Provera injections.
• You have barriers to completing the study, such as work or family commitments.
• You have symptoms of depression or excessive dietary restraint.
• You use tobacco products.
• You exercise more than 1 hour per day, 5 or more days per week.