Brain Dopamine Dynamics in Obesity

Prior treatment

• Current use of systemic hormone therapy, including oral, transdermal, or injectable estrogen or combined estrogen-progestogen preparations
• Radiation exposure for research purposes within the past year such that participation in this study would place them over guideline limits for annual radiation exposure (an effective dose of 5 rem received per year).
• Current, past or anticipated exposure to radiation in the workplace within one year
• Contraindications for MRI: metal implants incompatible with MRI, claustrophobia, large colored tattoos, or body weight \>285 pounds
• Current or past (within last year prior to enrollment) pharmacological obesity treatment
• Past surgical obesity treatment (bariatric surgery)
• Blood donation within 8 weeks prior to study

Other illness

• History of or current psychiatric disorder
• History of or current neurological disorder
• History of bleeding disorder or use of anticoagulants
• History of or current eating disorder (Eating Disorder Examination Questionnaire)
• Presence of type 1 or type 2 diabetes mellitus
• Uncontrolled thyroid disease
• Presence of any somatic disorder or medication use that interferes with brain functional networks or metabolic response to food
• Active oral or perioral conditions that may alter taste perception or compromise safety during gustometer use

Lab values

• Renal insufficiency (eGFR \<15 mL/min/1.73m²)

Age

• Childhood-onset obesity (onset before age 10 years)

Other

• Premenopausal status in women
• Smoking (current use of any tobacco or nicotine products)
• Elevated liver enzymes (\>2× the upper limit of normal)
• Anemia and/or Hematocrit \<35 vol%
• Lactose intolerance
• Shift work
• Current use of cannabis (any form), cocaine, amphetamines, or other recreational substances with known dopaminergic effects
• Heavy alcohol use, defined as \>15 standard drinks per week for men or \>8 standard drinks per week for women (National Institute on Alcohol Abuse and Alcoholism thresholds)
• Pacemaker in situ or other implanted electronic device
• Current use of structured meal replacement programs

• BMI 20-25 kg/m² (normal weight group) or BMI 30-45 kg/m² (obesity group)
• Stable body weight in the 3 months prior to enrollment (\<5%weight change)
• Male sex or postmenopausal female (defined as cessation of menstrual periods for ≥12 consecutive months or FSH \>25.8 mIU/mL)
• Able to read, write, and speak English
• Capable of giving informed consent