Inherited and Environmental Risks Acting on Body Weight

In study 1, participant twin pairs that differ in habitual diet intake, will complete an in-person study visit that includes an MRI of the brain and abdomen, body composition measurement, a blood draw and questionnaires. In study 2, a different set of participant twin pairs will complete 3 in-person study visits over 2 weeks, during which all meals will be provided by the study. Visits will include brain MRI, body composition measurements, blood draws and questionnaires.

Inclusion criteria

• Age 20-45 years
• Differs in habitual diet from co-twin (study 1).
• Willing to undergo 7-day overfeeding and hypocaloric feeding periods (study 2)
• Member of the Washington State Twin Registry

Exclusion criteria

• History of bariatric surgery or active participation in weight-loss program
• Major medical or neurological disorder (e.g., diabetes, multiple sclerosis)
• Known gallbladder disease, anemia, impaired thyroid, kidney or liver function or hypertriglyceridemia (>350 mg/dl) (study 2)
• Current use of weight-loss medications or other medications known to alter appetite (e.g., atypical anti-psychotics)
• High levels of vigorous physical activity (>300 min./week)
• Pregnancy, menopause, or breastfeeding
• Individuals with severe food allergies and dietary restrictions (e.g., vegan/vegetarian, gluten-free, others) (study 2)
• Co-twin unwilling or unable to participate
• MRI contraindication (e.g., implanted metal, claustrophobia)
• Lifetime eating disorder
• Current smoking or heavy alcohol use (≥ 2 drinks per day for females and ≥ 3 drinks per day for males)
• BMI > 45 kg/m2 (study 1)
• BMI > 35 kg/m2 (study 2)
• Weight > 350 pounds or determined to be safe by MRI tech (MRI limit)
• Inability to participate in a controlled diet program (study 2) or undergo other study procedures
• Non-English speaking-or-reading individuals