Healthy AdultsFLUXNCT07829237
FueL Use During eXercise in Males and Females
A study testing Pre-exercise carbohydrate beverage and Pre-exercise protein beverage in people with Healthy Adults, run by University of Toronto at 1 site in Canada.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 to 35 yearsHealthy volunteers can take part
- Conditions the study is for
- Healthy Adults
- What is being tested?
- Pre-exercise carbohydrate beverage and Pre-exercise protein beverage
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 24 participants
- Where
- 1 siteCanada
- Study dates
- 30 Sep 2026to 30 Jun 2027
- Phase
- Interventional
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 35 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- 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
Who cannot join
- 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
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Canada1 site, 1 recruiting
- Recruiting
Goldring Centre for High Performance Sport
Toronto, Ontario, M5S 2C9
Jenna Gillen, 4169783244, jenna.gillen@utoronto.ca
Victoria Bennett, 4169783244, victoria.bennett@mail.utoronto.ca
About this study
Official title: Influence of Pre-exercise Nutrition on Exercise Fuel Use in Males and Females
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.
Read the detailed description
Sex differences in substrate utilization during fasted endurance exercise are well established, with females generally demonstrating greater reliance on fat oxidation and lower carbohydrate utilization than males. However, exercise is frequently performed following nutrient ingestion, and it remains unclear whether sex differences in substrate utilization persist when carbohydrate or protein is consumed before exercise.
This randomized, counterbalanced crossover study will compare three pre-exercise nutritional conditions: carbohydrate (CHO), protein (PRO), and fasted/placebo (FAST). Participants will complete each condition separated by a minimum three-day washout. Following an overnight fast, participants will consume the assigned beverage and rest for 30 minutes before completing 90 minutes of cycling at 65% of VO2peak. This will be followed by a two-minute rest and a cycling time-to-task-failure test at 85% of maximal work rate.
The primary objective is to determine whether pre-exercise nutrition modifies sex differences in whole-body carbohydrate and fat oxidation and exogenous substrate oxidation during exercise. A secondary objective is to determine the effects of pre-exercise nutrition and sex on subsequent exercise performance.
- Conditions
- Healthy Adults
- Being tested
- Pre-exercise carbohydrate beverage, Pre-exercise protein beverage, Fasted control beverage
- Keywords
- exercise metabolism, substrate oxidation, exercise, nutrition, protein, carbohydrate
- Medical subject headings
- Motor Activity
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Pre-exercise carbohydrate beverageDietary 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.
Pre-exercise protein beverageDietary 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.
Fasted control beverageOther
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.
| Study group | Role | What they receive |
|---|---|---|
| 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. Receives: 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. Receives: 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. Receives: Other: Fasted control beverage |
What is being measured
The primary outcome is the main question the study is designed to answer.
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.
Measured: 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.
Measured: 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.
Measured: 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.
Measured: During the 90-min exercise bout
Secondary outcomes (1)
Time to task failure
Exercise performance will be assessed as time to volitional exhaustion during a cycling time-to-task-failure test performed at 85% of maximal work rate following the 90-minute moderate-intensity cycling bout.
Measured: Immediately following the 90-min exercise bout
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted18 Sep 2026
- Study start30 Sep 2026 (estimated)
- Primary completion30 Jun 2027 (estimated)
- Study completion30 Jun 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Healthy AdultsStudies of the same condition, open and under way.
- More trials run by University of TorontoThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Model description
- 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.
- Masking
- Double blind
- Who is masked
- Participant, Investigator
- Enrolment
- 24 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Toronto
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Jenna Gillen, University of Toronto
- Investigators
- Jenna Gillen, PhD, Principal investigator, University of Toronto
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07829237
- Sponsor's protocol ID
- HSREB50670
- Acronym
- FLUX
- Status last verified
- Sep 2026
- First submitted
- 14 Sep 2026
- Last updated
- 18 Sep 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 18 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Influence of Pre-exercise Nutrition on Exercise Fuel Use in Males and Females
- ClinicalTrials.gov ID
- NCT07829237
- Acronym / sponsor ID
- FLUX / HSREB50670
- Conditions
- Healthy Adults
- Keywords
- exercise metabolism, substrate oxidation, exercise, nutrition, protein, carbohydrate
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 24 participants (estimated)
- Lead sponsor
- University of TorontoUniversity, hospital or other
- Study start
- 30 Sep 2026 (estimated)
- Primary completion
- 30 Jun 2027 (estimated)
- Study completion
- 30 Jun 2027 (estimated)
- First posted
- 18 Sep 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Detailed description
Sex differences in substrate utilization during fasted endurance exercise are well established, with females generally demonstrating greater reliance on fat oxidation and lower carbohydrate utilization than males. However, exercise is frequently performed following nutrient ingestion, and it remains unclear whether sex differences in substrate utilization persist when carbohydrate or protein is consumed before exercise.
This randomized, counterbalanced crossover study will compare three pre-exercise nutritional conditions: carbohydrate (CHO), protein (PRO), and fasted/placebo (FAST). Participants will complete each condition separated by a minimum three-day washout. Following an overnight fast, participants will consume the assigned beverage and rest for 30 minutes before completing 90 minutes of cycling at 65% of VO2peak. This will be followed by a two-minute rest and a cycling time-to-task-failure test at 85% of maximal work rate.
The primary objective is to determine whether pre-exercise nutrition modifies sex differences in whole-body carbohydrate and fat oxidation and exogenous substrate oxidation during exercise. A secondary objective is to determine the effects of pre-exercise nutrition and sex on subsequent exercise performance.
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Crossover
- Masking
- Double blind (participant, investigator)
- Number of arms
- 3
- Model description
- 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.
| Arm | Type | Receives |
|---|---|---|
| Carbohydrate (CHO) | Experimental | Dietary Supplement: Pre-exercise carbohydrate beverageParticipants 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. |
| Protein (PRO) | Experimental | Dietary Supplement: Pre-exercise protein beverageParticipants 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. |
| Fasted (FAST) | Placebo comparator | Other: Fasted control beverageParticipants 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. |
Who may qualify
- Ages
- 18 to 35 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (7 listed)
- 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
Key exclusion criteria (1 listed)
- 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
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Pre-exercise carbohydrate beverageA 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. | Dietary supplement | Carbohydrate (CHO) |
| Pre-exercise protein beverageA 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. | Dietary supplement | Protein (PRO) |
| Fasted control beverageA 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. | Other | Fasted (FAST) |
Primary outcome
Whole-body carbohydrate oxidation
Time frame: During the 90-minute exercise bout
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.
Whole-body fat oxidation
Time frame: During the 90-min exercise bout
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.
Exogenous glucose oxidation
Time frame: During the 90-min exercise bout
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.
Exogenous leucine oxidation
Time frame: During the 90-min exercise bout
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.
1 secondary outcome
Time to task failure
Time frame: Immediately following the 90-min exercise bout
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 18 Sep 2026.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Jenna Gillen, PhD principal investigator
University of Toronto
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Pre-exercise carbohydrate beverage and Pre-exercise protein beverage in people with Healthy Adults, run by University of Toronto at 1 site in Canada.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 1 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 18 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Canada. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Jenna Gillen, PhD (4169783244, jenna.gillen@utoronto.ca), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Whole-body carbohydrate oxidation (time frame: During the 90-minute exercise bout). The study lists 4 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Sep 2026.