This randomized controlled crossover study will examine the acute effects of pistachio consumption on postprandial metabolic responses in adults with overweight or obesity. Participants will complete two experimental conditions in randomized order. In one condition, participants will consume 30 g of pistachios with a standardized meal, and in the other condition they will receive an isocaloric refined-carbohydrate control condition with the standardized meal.
The study will evaluate postprandial insulin and glucose responses over approximately 3 hours after meal consumption. Additional outcomes will include continuous glucose monitoring measures, blood lipid responses, appetite and satiety ratings, and exploratory measures related to insulin sensitivity and gastrointestinal hormone responses. The study is designed to determine whether pistachio consumption alters acute metabolic responses compared with an isocaloric refined-carbohydrate control in adults with overweight or obesity.
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.
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.
Crossover
Pistachio Co-consumption
Other interventionParticipants will consume 30 g of shelled, lightly salted pistachios together with a standardized high-glycemic breakfast meal. The pistachios and standardized breakfast meal will be consumed within a fixed 10-minute meal period.
Refined-Carbohydrate Control Co-consumption
Other interventionParticipants will consume an isocaloric refined-carbohydrate control food together with the same standardized high-glycemic breakfast meal. The control food will be matched to the pistachio condition for energy content as closely as possible while providing minimal fiber, protein, unsaturated fat, and bioactive compounds.
Postprandial Insulin Incremental Area Under the Curve (iAUC)
Postprandial plasma insulin will be measured at 0, 30, 60, 90, 120, 150, and 180 minutes after meal consumption. Insulin incremental area under the curve (iAUC) from 0 to 180 minutes will be calculated using the trapezoidal rule with baseline subtraction. Insulin iAUC will be compared between the pistachio and refined-carbohydrate control conditions.
Postprandial Plasma Glucose Incremental Area Under the Curve (iAUC)
Plasma glucose concentrations will be measured at 0, 30, 60, 90, 120, 150, and 180 minutes after meal consumption. Glucose iAUC from 0 to 180 minutes will be calculated using the trapezoidal rule with baseline subtraction and compared between conditions.
Continuous Glucose Monitoring Time in Range
Percentage of CGM glucose readings within the predefined range of 70-180 mg/dL during the postprandial laboratory monitoring period will be calculated and compared between the pistachio and refined-carbohydrate control conditions.
Continuous Glucose Monitoring Mean Glucose
Mean interstitial glucose concentration measured by continuous glucose monitoring during the postprandial laboratory monitoring period will be calculated and compared between conditions.
Continuous Glucose Monitoring Glycemic Variability
Glycemic variability will be assessed using the coefficient of variation (CV) of CGM-derived interstitial glucose concentrations during the postprandial monitoring period and compared between conditions.
Postprandial Plasma Triglycerides
Plasma triglyceride concentrations will be assessed before and after the test meal to evaluate the acute postprandial lipid response and compared between the pistachio and refined-carbohydrate control conditions.
Postprandial Glucagon-Like Peptide-1 (GLP-1) Concentrations
GLP-1 concentrations will be assessed from stored plasma samples to explore the acute incretin response to the pistachio and refined-carbohydrate control conditions, if funding and sample availability permit.
Postprandial Glucose-Dependent Insulinotropic Polypeptide (GIP) Concentrations
GIP concentrations will be assessed from stored plasma samples to explore the acute incretin response to the pistachio and refined-carbohydrate control conditions, if funding and sample availability permit.
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