The investigators will conduct a randomized trial to evaluate the effectiveness of 3 levels of recommended exercise in initially overweight and obese sedentary men and women on the prevention of weight regain. Participants will complete a 3 mo. weight loss intervention of decreased energy intake (EI) and increased energy expenditure (100 minutes of physical activity per week). Participants achieving clinically significant weight loss (> 5% of initial weight), will be randomly assigned to 12 mos. of exercise at levels of energy expenditure of exercise (EEEx) recommended by Health and Human Services (HHS), American College of Sports Medicine(ACSM), Institute of Medicine (IOM): 150, 225, or 300 minutes per week. Major outcome assessments will occur prior to weight loss (-3 mos.), at completion of weight loss (0 mos.), at the midpoint (6 mos.), and completion of weight maintenance (12 mos.).

The investigators propose a randomized trial in 287 overweight and obese, sedentary adults (at least 50% women). Participants achieving clinically significant weight loss (≥5%) following a 3 mo. reduced energy diet and a program of PA (100 min/wk) will be randomly assigned to either maintain exercise at 150 min/wk. or increase exercise to 225 min/wk or 300 min/wk. while consuming a weight gain prevention diet over a 12 mo. period. Exercise will be verified (combination of on-site and HR monitor) and EEEx will be measured at 5 mo. intervals beginning at mo. 5. In-person behaviorally based clinic meetings will be conducted weekly during the 3 mo. weight loss period (-3 to 0 mos.) and during the first 3 mos. of the weight regain prevention period. During the final 9 mos. of weight regain prevention, clinics will be held bi-monthly using group conference calls. We have not proposed to randomize participants to a true control group (i.e. no exercise or diet) following the 3 mo. weight loss program as published data indicates significant weight regain in individuals receiving no follow-up treatment after weight loss.

Inclusion Criteria:

• Age 21 to 55 years.
• BMI of 25 to 45.0.
• Clearance for participation from their Primary Care Physician (PCP)

Exclusion Criteria:

• Participation in a research project involving weight loss or exercise in the previous 6 mos., as these proximal experiences may impact the results of this study.
• Participation in a regular exercise program (i.e., > 500 kcal/wk. of planned activity as estimated by questionnaire)
• Not weight stable (+ or - 4.5 kg) for 3 mos. prior to intake.
• Unwilling to be randomized to 1 of 3 exercise groups subsequent to weight loss.
• Pregnant during the previous 6 mos., lactating, or planned pregnancy in the following 15 mos.
• Serious medical risk such as type 1 diabetes, cancer, recent cardiac event (i.e., heart attack, angioplasty, etc.). This is determined by the individual's physician via the clearance to participate in the investigation and the health history (Appendix) interpreted by the staff physician.
• Eating disorders as determined by the Eating Attitudes Test using a score of 20 or greater
• Current treatment for psychological problems, or taking psychotropic medications
• Medications known to significantly affect weight (gain or loss).
• Adherence to specialized diet regimens, i.e., multiple food allergies, vegetarian, macrobiotic, etc.
• Do not have access to grocery shopping and meal preparation (i.e. those in military, college with cafeteria plan, etc.).