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.