FueL Use During eXercise in Males and Females

NCT07829237 | Recruiting

• 1 other identifier: HSREB50670
• Study Type: interventional
• Target: 24
• Locations: 1 country
• Sites: 1

Brief Summary

This study will investigate whether pre-exercise nutrition influences sex differences in fuel utilization during endurance exercise. Twenty-four recreationally active adults (12 females and 12 males) will complete three experimental exercise trials in a randomized, counterbalanced crossover design. Before each trial, participants will consume either a carbohydrate beverage, a protein-based beverage, or a flavour-matched non-caloric beverage representing the fasted condition. Thirty minutes later, participants will complete 90 minutes of moderate-intensity cycling followed by a cycling time-to-task-failure test. Whole-body carbohydrate and fat oxidation, exogenous substrate oxidation, blood metabolites, and exercise performance will be assessed.

Conditions

Healthy Adults

Keywords

exercise metabolism; substrate oxidation; exercise; nutrition; protein; carbohydrate

Outcome Measures

Primary Outcomes (4)

• Whole-body carbohydrate oxidation

  Whole-body carbohydrate oxidation will be calculated from oxygen consumption (VO2) and carbon dioxide production (VCO2) measured by indirect calorimetry during 90 minutes of moderate-intensity cycling. Carbohydrate oxidation will be compared between the carbohydrate, protein, and fasted conditions and between females and males.

  During the 90-minute exercise bout

• Whole-body fat oxidation

  Whole-body fat oxidation will be calculated from VO2 and VCO2 measured by indirect calorimetry during 90 minutes of moderate-intensity cycling. Fat oxidation will be compared between the carbohydrate, protein, and fasted conditions and between females and males.

  During the 90-min exercise bout

• Exogenous glucose oxidation

  Exogenous glucose oxidation will be determined during the carbohydrate condition using breath 13CO2 enrichment following ingestion of \[U-13C6\]-D-glucose. Breath samples will be analyzed by isotope ratio mass spectrometry, and exogenous glucose oxidation will be calculated using 13CO2 enrichment and carbon dioxide production.

  During the 90-min exercise bout

• Exogenous leucine oxidation

  Exogenous leucine oxidation will be determined during the protein condition using breath ¹³CO₂ enrichment following ingestion of L-\[1-¹³C\]leucine. Breath samples will be analyzed by isotope ratio mass spectrometry, and exogenous leucine oxidation will be calculated using breath ¹³CO₂ enrichment and carbon dioxide production.

  During the 90-min exercise bout

Secondary Outcomes (1)

• Time to task failure

  Immediately following the 90-min exercise bout

Study Arms (3)

Carbohydrate (CHO)

EXPERIMENTAL

Participants will consume a carbohydrate beverage following an overnight fast. Thirty minutes after beverage consumption, participants will complete 90 minutes of cycling at 65% of VO2peak, followed by a 2-minute rest and a cycling time-to-task-failure test at 85% of maximal work rate.

Dietary Supplement: Pre-exercise carbohydrate beverage

Protein (PRO)

EXPERIMENTAL

Participants will consume a protein-based beverage following an overnight fast. Thirty minutes after beverage consumption, participants will complete 90 minutes of cycling at 65% of VO2peak, followed by a 2-minute rest and a cycling time-to-task-failure test at 85% of maximal work rate.

Dietary Supplement: Pre-exercise protein beverage

Fasted (FAST)

PLACEBO COMPARATOR

Participants will remain fasted and consume a non-caloric, flavour-matched beverage. Thirty minutes after beverage consumption, participants will complete 90 minutes of cycling at 65% of VO2peak, followed by a 2-minute rest and a cycling time-to-task-failure test at 85% of maximal work rate.

Other: Fasted control beverage

Interventions

Pre-exercise carbohydrate beverage DIETARY_SUPPLEMENT

A carbohydrate beverage providing 1 g glucose/kg body mass, enriched with 1 mg/kg body mass \[U-13C6\]-D-glucose for assessment of exogenous carbohydrate oxidation, with calorie-free flavouring. The beverage will be consumed within 5 minutes, 30 minutes before exercise.

Carbohydrate (CHO)

Pre-exercise protein beverage DIETARY_SUPPLEMENT

A protein-based beverage providing 0.45 g protein/kg body mass and supplemented with 0.24 g fat/kg body mass to match the energy content of the carbohydrate condition. The beverage is enriched with L-\[1-13C\]leucine and flavour-matched to the carbohydrate beverage. It will be consumed within 5 minutes, 30 minutes before exercise.

Protein (PRO)

Fasted control beverage OTHER

A non-caloric beverage consisting of water and sugar-free flavouring, flavour-matched to the carbohydrate beverage. The beverage will be consumed within 5 minutes following an overnight fast, 30 minutes before exercise.

Fasted (FAST)

Eligibility Criteria

• Age: 18 Years - 35 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Participating in ≥150 minutes of moderate-to-vigorous physical activity per week
• VO₂peak classified as "good" or above based on American College of Sports Medicine normative values: \>35.0 mL/kg/min for females and \>39.0 mL/kg/min for males
• Body mass index (BMI) between 18 and 27 kg/m²
• Participating in 3-5 structured exercise sessions per week
• Weight stable, defined as within ±2 kg for at least 6 months
• Non-smoker
• Females must be eumenorrheic

You may not qualify if:

• Polycystic ovarian syndrome (PCOS) or endometriosis Current use of oral contraceptives or oral contraceptive use within the previous 3 months Diagnosed cardiovascular or metabolic disease Hypergonadism or hypogonadism Use of medications for management of blood glucose or lipid metabolism Pregnant or \<12 months postpartum Lactating or breastfeeding within 3 months of study commencement Menopausal Recreational tobacco smoking Inability to complete the study exercise protocols or comply with pre-trial dietary or physical activity controls Use of medications that may affect substrate metabolism, including corticosteroids or non-steroidal anti-inflammatory drugs (NSAIDs) Currently following a low-carbohydrate diet, such as a ketogenic or Atkins diet

Sponsors & Collaborators

• University of Toronto: lead

Study Sites (1)

Goldring Centre for High Performance Sport

Toronto, Ontario, M5S 2C9, Canada

RECRUITING

MeSH Terms

Conditions

Motor Activity

Condition Hierarchy (Ancestors)

Behavior

Study Officials

• Jenna Gillen, PhD

  University of Toronto

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Jenna Gillen, PhD

CONTACT

4169783244; jenna.gillen@utoronto.ca

Victoria Bennett

CONTACT

4169783244; victoria.bennett@mail.utoronto.ca

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: PARTICIPANT, INVESTIGATOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Associate Professor

Model Details: Each participant will complete three pre-exercise nutrition conditions (carbohydrate, protein, and fasted/placebo) in a randomized, counterbalanced order, with a minimum 3-day washout period between conditions.

Study Record Dates

• First Submitted: September 14, 2026
• First Posted: September 18, 2026
• Study Start: September 30, 2026
• Primary Completion (Estimated): June 30, 2027
• Study Completion (Estimated): June 30, 2027
• Last Updated: September 18, 2026

Record last verified: 2026-09

Data Sharing

• IPD Sharing: Will not share

Locations

CA (1)