Inclusion Criteria:

   - Age: > 18 years of age

   - Women: Pre-menopausal (self-report) and <50 years of age

   - Men: <50 years of age

   - BMI (body mass index): 27-40 kg/m2 (need to lose >10% body weight to achieve healthy
   BMI)

   - Body weight stable for the last two months, and not actively on a weight loss plan

   - No plans to move from the area over the next two years

   - Available and able to participate in the evaluations and intervention for the study
   period

   - Willing to accept random assignment

   - To enhance study generalizability, people on medications not noted below as specific
   exclusions can

   - participate if they have been stable on such medications for at least three months

   - Ability and willingness to give written informed

   - No known active psychiatric illness

Exclusion Criteria:

Subjects with the following conditions will be excluded (determined by self-report):

   - Pregnant, lactating, within 6 months post-partum, or planning to become pregnant in
   the next 2 years

   - Diabetes (type 1 and 2) or history of gestational diabetes or on hypoglycemic
   medications for any other indication

   - Prevalent diseases: Malabsorption, renal or liver disease, active neoplasms, recent
   myocardial infarction (<6 months)(patient self-report and, if available, review of
   labs from primary care provider)

   - Smokers (because of effect on weight and lipids)

   - History of serious arrhythmias, or cerebrovascular disease

   - Uncontrolled hyper- or hypothyroidism (TSH not within normal limits)

   - Medications: Lipid lowering, antihypertensive medications, and those known to affect
   weight/energy expenditure

   - Excessive alcohol intake (self-reported, >3 drinks/day)

   - Musculoskeletal disorders precluding regular physical activity

   - Unable to follow either of the two study diets for reasons of food allergies or other
   (e.g., vegan)

   - Currently under psychiatric care, or taking psychiatric medications

   - Inability to communicate effectively with study personnel