Pistachio Snacking and Metabolic Flexibility

January 5, 2026 updated by: Katie Hirsch, University of South Carolina

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

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
60

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Locations

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

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

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

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

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

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
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

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
resting metabolism
Time Frame: Day 0 and Day 5
resting metabolic rate (RMR) and substrate utilization (RER) via indirect calorimetry
Day 0 and Day 5
exercise metabolic flexibility
Time Frame: Day 0 and Day 5
substrate metabolism (RER; indirect calorimetry) throughout a submaximal, graded exercise test
Day 0 and Day 5
post-exercise metabolism
Time Frame: Day 0 and Day 5
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

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Caloric Intake
Time Frame: Day 0 and Day 4
Average calorie intake (kcal) via 24-hr diet record
Day 0 and Day 4
Carbohydrate Intake
Time Frame: Day 0 and Day 4
Average carbohydrate intake (grams) via 24-hr diet record
Day 0 and Day 4
Protein Intake
Time Frame: Day 0 and Day 4
Average protein intake (grams) via 24-hr diet record
Day 0 and Day 4
Fat Intake
Time Frame: Day 0 and Day 4
Average fat intake (grams) via 24-hr diet record
Day 0 and Day 4

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Physical Activity
Time Frame: daily continuous (Day 0 to Day 5)
Daily (24-hr) steps and intensity minutes via wrist activity tracker
daily continuous (Day 0 to Day 5)
Sleep Quantity
Time Frame: Nightly (Day 0 to Day 5)
Nightly sleep quantity (total time spent asleep; minutes) via wrist worn activity tracker.
Nightly (Day 0 to Day 5)
Sleep Quality
Time Frame: Nightly (Day 0 to Day 5)
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
Time Frame: Day 0 and Day 5
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
Time Frame: Daily (Day 1 to Day 4)
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

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
University of South Carolina

Collaborators

Collaborators

An organization other than the sponsor that provides support for a clinical study. This support may include activities related to funding, design, implementation, data analysis, or reporting.
American Pistachio Growers

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Principal Investigator: Katie R Hirsch, PhD, University of South Carolina

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
September 1, 2025

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
August 1, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
December 31, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
December 17, 2025

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
January 5, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
January 14, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
January 14, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
January 5, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant 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

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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