Effects of Pistachios on Postprandial Metabolic Responses in Adults With Overweight or Obesity

Inclusion Criteria: * Age 18-35 years, male or female, and able to provide informed consent. * BMI ≥25.0 kg/m². Waist circumference and BIA-derived body composition will also be assessed during screening and considered with BMI to help confirm that elevated BMI reflects excess adiposity rather than primarily high muscularity. * Weight stable, defined as no intentional weight loss or body weight change \>3 kg during the previous 3 months. * Generally healthy and not currently taking medications known to substantially affect glucose metabolism, insulin secretion, insulin sensitivity, appetite, or body weight. Stable thyroid hormone replacement for a well-controlled thyroid condition is not automatically exclusionary. * Able to complete a 10-12-hour overnight fast and refrain from vigorous exercise and alcohol for 24 hours before each test meal visit. * Able and willing to consume pistachios, the refined-carbohydrate control food, and the standardized breakfast meal. Exclusion Criteria: * Known diagnosis of type 1 or type 2 diabetes. Individuals with known prediabetes will not be excluded. * Clinically significant cardiovascular disease, including prior myocardial infarction or stroke, uncontrolled hypertension, clinically significant arrhythmia, or another cardiovascular condition that could make participation unsafe or meaningfully affect study outcomes. * Chronic kidney disease or another major medical condition that could make participation unsafe or meaningfully affect metabolic outcomes. * Current participation in a weight-loss program, use of weight-loss medications, or history of bariatric surgery within the past year. * Known allergy or intolerance to pistachios, tree nuts, peanuts/peanut butter, wheat/gluten, orange juice/citrus, or any other study-meal ingredient. * Celiac disease, Crohn's disease, ulcerative colitis, or another clinically significant gastrointestinal or malabsorption condition that could affect digestion, nutrient absorption, or metabolic responses. * Current ketogenic, very-low-carbohydrate, or medically prescribed diet that could meaningfully interfere with the standardized feeding protocol or metabolic outcomes. * Participation in another clinical research trial within the past 3 months that could affect participant safety or study outcomes. * Recent significant illness, infection, or surgery within the past 4 weeks that could affect participant safety or study outcomes. * Current or prior clinically significant eating disorder that, in the investigator's judgment, could make participation unsafe or interfere with the feeding protocol. * Current smoking, frequent nicotine use, or excessive alcohol use. * Pregnancy, planned pregnancy during the study period, or lactation. * Any condition or medication that, in the investigator's judgment, would make participation unsafe or interfere with outcome measures.