1. the volunteer (male or non-pregnant female, any ethnicity) must be >18 years of age.

2. the volunteer must either have a body mass index of 25.0-35.0 kg/m2 or the combination of a body mass index of 18.5-24.9 kg/m2 and two or more previously or currently measured symptoms of the metabolic syndrome (fasting glucose≥110 mg/dl, triglycerides≥150 mg/dl, high-density lipoprotein cholesterol<40 mg/dl in males or <50 mg/dl in females, systolic blood pressure≥130 mmhg or diastolic blood pressure≥85 mmhg, or waist circumference≥40 inches in males or ≥36 inches in females [glucose and cholesterol levels may be self-reported]).

3. the volunteer has not routinely participated in caloric restriction (deliberate limitation of caloric intake of <80% than the fda-recommended daily caloric intake) within the last 2 years, has not participated in extended fasting (>12 hours at a time) for at least a year, and does not deliberately skip meals as a routine dietary practice.

1. body mass index <18.5 or >35 kg/m2.

2. current active cancer treatment, treatment with immunosuppressive medications, or solid organ transplantation within 1 year.

3. presence of immunosuppressive disease, myocardial infarction, peripheral vascular disease, or stroke within the past year.

4. use of insulin.

5. although it is unlikely fasting will harm the pregnant or lactating woman, the dietary restrictions placed on the participant for the duration of the study may conflict with dietary recommendations for pregnant or lactating women. women of child bearing potential, therefore, will meet an exclusion if they become pregnant.