Scientists are examining the genetic and environmental influences on appetite and weight gain. The main purpose of this study is to look at how genetic and environmental factors may influence how the brain regulates appetite and food intake. Understanding how the brain regulates appetite and food intake may eventually lead to new ways to help people avoid obesity or lose weight.

Inclusion Criteria:

• Ability and willingness to come with their twin to the University of Washington (Seattle)
• Additional Criteria for Aim 1 random sample only: Member of randomly selected MZ pair or
• Additional criteria for Aim 2 random sample only: One member of MZ or same-sex DZ pair with BMI of at least 30 kg/m^2
• Additional criteria for Aim 3 sample only: Member of randomly selected MZ pair, and not BMI discordant ≥ 5 kg/m^2

Exclusion Criteria:

• History of weight loss surgery or active participation in weight loss program
• Major medical problem (e.g., diabetes, cancer)
• Current use of weight loss medications or other medications known to alter appetite
• Pregnancy or menopause
• MRI contraindication (i.e., implanted metal, claustrophobia)
• Lifetime eating disorder
• Current smoking
• Current heavy alcohol use (≥2 drinks per day for females and ≥ 3 drinks per day for males)
• Self-reported weight >330 pounds at time of phone screening. MRI cannot accommodate all shapes or weights. Inability to have MRI does not exclude subject from participating in other study procedures.
• BMI < 18.5 or > 45 kg/m^2
• Allergies to study foods or inability to taste
• Twins were raised apart
• Co-twin not eligible or not willing to participate

Monozygotic and dizygotic twins recruited from the University of Washington Twin Registry