Compare intermittent versus continuous calorie restriction to learn more about these eating plans and determine whether they are useful and effective to lose weight and keep it off.

The purpose of this study is to provide evidence for the feasibility of an alternative weight control strategy by comparing two diets to see how intermittent calorie restriction compares to continuous or daily calorie restriction for weight loss in 35 adults with overweight or obesity. These diets will be incorporated into a comprehensive and intensive weight management program involving weekly health education meetings, regular diet and physical activity tracking, and feedback from a registered dietitian.

Each intervention includes 3 months of weight loss and 3 months of weight maintenance.

Group 1: Follow a low-calorie diet every day (1,200 - 1,500 calories daily)

Group 2: Follow an intermittent very-low calorie diet (500-800 calories). Participants in this group will alternate between days of 500-800 calories and days of structured eating using healthy eating principles.

Inclusion Criteria:

1. Age 21-65 years.
2. BMI 25-35. Patients with a BMI less than 25 are not classified as overweight and individuals with a BMI >35 may require more aggressive weight management strategies.
3. Clearance for participation from their PCP.

Exclusion Criteria:

1. Participation in a research project or formal program involving weight loss or exercise in the previous 6 mos., as these proximal experiences may impact the results of this study.
2. Participation in a regular exercise program (i.e., > 500 kcal/wk. of planned activity as estimated by questionnaire [34].
3. Not weight stable (-/+ 5%) for 6 mos. prior to intake. This will be determined by phone screen and self-report on the health history questionnaire
4. Unwilling to be randomized to one of two diet strategies for weight loss.
5. Pregnant during the previous 6 mos., lactating, or planned pregnancy in the following 6 mos.
6. Serious medical risk (e.g. diabetes, cancer, cardiovascular disease) as determined by the individual's physician via the clearance to participate in the investigation.
7. Disordered eating as determined by the Eating Attitudes Test using a score of 20 or greater [35]. This score indicates the need for counseling outside the scope of this study.
8. Current treatment for psychological problems, or taking psychotropic medications. Addressing psychological problems is outside the scope of this study.
9. Medications known to significantly influence weight.
10. Adherence to specialized diet regimens (e.g., multiple food allergies, vegan, etc.)
11. Do not have access to or independence over grocery shopping and meal preparation (i.e. those in military, college with cafeteria plan, etc.).
12. If participants have recently undergone CT (Computed Tomography), PET, fluoroscopic, or nuclear medicine studies within the past year.