Pistachio Snacking and Metabolic Flexibility

Effects of Pistachio Snacking on Metabolic Flexibility in Healthy Overweight and Obese Adults

The purpose of this study is to evaluate the effects of pistachio snacking on metabolic flexibility (at rest, during exercise, and in post-exercise recovery) in healthy overweight and obese adults. Secondary goals include evaluating effects on changes in diet quality, sleep characteristics, physical activity, and hormonal health in women. In randomized order, participants will complete four days of pistachio snacking and four days of normal dietary habits (control). For both conditions, primary outcomes of resting substrate metabolism, metabolic flexibility during exercise, and post-exercise substrate metabolism will be measured pre-post intervention via indirect calorimetry. Secondary outcome of diet quality (kcal, carb, fat, protein) will be measured pre-post intervention via diet log. Exploratory outcomes of daily physical activity (steps, intensity), nightly sleep characteristics (quantity, quality, latency, efficiency), and daytime sleepiness and hunger.

Study Overview

• Status: Recruiting
• Conditions: Healthy Participants; Physically Inactive; Overweight or Obese; Poor Sleep Quality; Overweight (BMI > 25); Obese But Otherwise Healthy Participants; Obese Patients (BMI ≥ 30 kg/m²)
• Intervention / Treatment: Other: Pistachio

• Study Type: Interventional
• Enrollment (Estimated): 60
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Callie Unrein, MS; Phone Number: 803-777-5478; Email: sustainlab@mailbox.sc.edu

Study Locations

• United States
  • South Carolina
    • Columbia, South Carolina, United States, 29208
      • Recruiting
      • Public Health Research Center: Clinical Exercise Research Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Males and Females
• Age: 25-45 years
• Overweight or obese (BMI=25.0-34.9 kg/m²)
• Poor sleep quality (Pittsburgh Sleep Quality Index ≥ 5)
• Healthy (no diagnosed metabolic, cardiovascular, sleep, or other health condition that may significantly alter metabolism, sleep, or ability to participate in the exercise test)
• Not meeting weekly physical activity recommendations (<150 min moderate-intensity exercise, <75 minutes of vigorous-intensity exercise, and <2 days of strength training)
• Not following a diet that is restrictive or eliminates certain food group/types

Exclusion Criteria:

• Allergies to nuts, especially tree nuts
• Has a pacemaker
• Following a diet that is restrictive or eliminates certain food group/types
• Self-repoted health or disease state that may influence study outcomes, including known metabolic or endocrine disorder (e.g. prediabetes, type 1 or type 2 diabetes, or polycystic ovary syndrome), cardiovascular diseases, neuromuscular disorders, musculoskeletal disorders; current or recent history of cancer/cancer treatment (within the past year)
• History of gastrointestinal surgery, hysterectomy
• For women: pregnant or thinking of becoming pregnant during the time of participation, pregnant within the last year, currently breastfeeding, or known to be perimenopausal

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Pistachio; Four days of pistachio snacking, to be consumed mid-morning (1oz; 9-11am), mid-afternoon (1oz; 2-4pm), and pre-sleep (0.5 oz; within 1hr of bedtime), while otherwise maintaining normal dietary habits. An addition snack will be consumed post-exercise (0.5oz).	Other: Pistachio; Roasted, lightly salted, pistachio kernels (no shell)
No Intervention: Control; Maintain normal dietary habits for four days.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
resting metabolism	resting metabolic rate (RMR) and substrate utilization (RER) via indirect calorimetry	Day 0 and Day 5
exercise metabolic flexibility	substrate metabolism (RER; indirect calorimetry) throughout a submaximal, graded exercise test	Day 0 and Day 5
post-exercise metabolism	Energy expenditure and substrate metabolism (RER) measured at 0, 30, 60, 90min post-exercise via indirect calorimetry	Day 0 and Day 5

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Caloric Intake	Average calorie intake (kcal) via 24-hr diet record	Day 0 and Day 4
Carbohydrate Intake	Average carbohydrate intake (grams) via 24-hr diet record	Day 0 and Day 4
Protein Intake	Average protein intake (grams) via 24-hr diet record	Day 0 and Day 4
Fat Intake	Average fat intake (grams) via 24-hr diet record	Day 0 and Day 4

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Physical Activity	Daily (24-hr) steps and intensity minutes via wrist activity tracker	daily continuous (Day 0 to Day 5)
Sleep Quantity	Nightly sleep quantity (total time spent asleep; minutes) via wrist worn activity tracker.	Nightly (Day 0 to Day 5)
Sleep Quality	Nightly sleep quality (time spent in deep sleep (minutes), REM sleep (minutes), and light sleep (minutes)) via wrist worn activity tracker.	Nightly (Day 0 to Day 5)
Daytime sleepiness	Subjective likelihood of falling asleep in various situations via Epworth Sleepiness Scale. In this eight question survey, questions are rated on a scale of 0 (very unlikely) to 3 (very likely), with a total score of 0-9 indicating low daytime sleepiness, 10-15 indicating moderate daytime sleepiness, and 16-24 indicating severe daytime sleepiness.	Day 0 and Day 5
Subjective hunger	Degree of hunger/fullness (Visual Analog Scale) mid-morning (post-snack), late morning (a few hours post snack), and mid-afternoon (pre-snack).	Daily (Day 1 to Day 4)

Collaborators and Investigators

• Sponsor: University of South Carolina
• Collaborators: American Pistachio Growers
• Investigators: Principal Investigator: Katie R Hirsch, PhD, University of South Carolina

Study record dates

Study Major Dates

• Study Start (Actual): September 1, 2025
• Primary Completion (Estimated): August 1, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: December 17, 2025
• First Submitted That Met QC Criteria: January 5, 2026
• First Posted (Actual): January 14, 2026

Study Record Updates

• Last Update Posted (Actual): January 14, 2026
• Last Update Submitted That Met QC Criteria: January 5, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: metabolism; metabolic flexibility; diet quality; Pistachio; Tree Nuts; snacking
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Signs and Symptoms; Overweight; Obesity
• Other Study ID Numbers: Pro00145186

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: data may be shared upon reasonable request.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No