Testing the Adipose Expandability Hypothesis in Vivo During Overfeeding

Inclusion Criteria: * Men and pre-menopausal women * 18-42 years of age * BMI 23-35 kg/m2 (± 0.5 will be accepted) * Are willing to drink deuterium-labeled water (2H2O) for 8 weeks * Are willing to be randomized to either a CTL or 30% OF group * For women, if not using pharmaceutical (hormonal) contraception (i.e. birth control pills, vaginal ring, injections, or implant), must agree to use either a double barrier method as a form of birth control to prevent pregnancy (i.e. male condom with spermicide, with or without cervical cap or diaphragm); use implants or intrauterine contraceptive devices; have a tubal ligation (surgically sterile); practice abstinence; or be in an established relationship with a vasectomized or same sex partner during the entire duration of the study * Must be willing to adhere to all study procedures, including attendance at all study visits * If enrolled, agree to maintain the same level of physical activity throughout the duration of the study * Must be willing to have blood stored for future research Exclusion Criteria: * Unstable weight in the last 3 months (± \~5% weight change) * Diagnosis of Type 1 or 2 diabetes or a fasting blood glucose \> 110 mg/dL * Average screening blood pressure \> 140/90 mmHg * Diagnosis of major organ disease (e.g. heart, kidney, lung, thyroid, liver disease) or abnormal liver enzymes that are, in the opinion of the MI, clinically significant and represent a problem for study inclusion. * Self-reported positive test for human immunodeficiency virus, hepatitis B or hepatitis C * Any current or previous eating disorders * Chronic use of systemic glucocorticoids (steroids), systemic adrenergic-stimulating agents, beta-blockers, antipsychotic medications, thiazolidinediones and other medications that may cause clinically significant weight gain or loss) * Chronic use of prescription weight loss medications or over the counter weight loss medications which, in the opinion of the MI, will impact the study * Chronic use of anti-depressant medications for less than 3 months * Chronic smokers or users of tobacco products who cannot abstain for the duration of the inpatient visits * Previous bariatric or other surgeries for obesity * Had cancer in the last 5 years (some skin cancers acceptable) * Pregnancy, breastfeeding, or planned pregnancy for the upcoming 6 months * Partial or full hysterectomy * PCOS * Diagnosed psychotic conditions.