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FueL Use During eXercise in Males and Females (FLUX)

14 september 2026 bijgewerkt door: Jenna Gillen, University of Toronto

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.

Studie Overzicht

Toestand

Werving

Conditie

Interventie / Behandeling

Gedetailleerde beschrijving

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.

Studietype

Ingrijpend

Inschrijving (Geschat)

24

Fase

  • Niet toepasbaar

Contacten en locaties

In dit gedeelte vindt u de contactgegevens van degenen die het onderzoek uitvoeren en informatie over waar dit onderzoek wordt uitgevoerd.

Studiecontact

Studie Contact Back-up

Studie Locaties

Deelname Criteria

Onderzoekers zoeken naar mensen die aan een bepaalde beschrijving voldoen, de zogenaamde geschiktheidscriteria. Enkele voorbeelden van deze criteria zijn iemands algemene gezondheidstoestand of eerdere behandelingen.

Geschiktheidscriteria

Leeftijden die in aanmerking komen voor studie

18 jaar tot 35 jaar (Volwassen)

Accepteert gezonde vrijwilligers

Ja

Geslachten die in aanmerking komen voor studie

Allemaal

Beschrijving

Inclusion Criteria:

  • 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

Exclusion Criteria:

  • 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

Studie plan

Dit gedeelte bevat details van het studieplan, inclusief hoe de studie is opgezet en wat de studie meet.

Hoe is de studie opgezet?

Ontwerpdetails

  • Primair doel: Fundamentele wetenschap
  • Toewijzing: Gerandomiseerd
  • Interventioneel model: Crossover-opdracht
  • Masker: Dubbele

Wapens en interventies

Deelnemersgroep / Arm
Interventie / Behandeling
Experimenteel: Carbohydrate (CHO)

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.
Voedingssupplement: Pre-exercise carbohydrate beverage

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.
Experimenteel: Protein (PRO)

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.
Voedingssupplement: Pre-exercise protein beverage

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.
Placebo-vergelijker: Fasted (FAST)

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.
Ander: Fasted control beverage

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.

Wat meet het onderzoek?

Primaire uitkomstmaten

Uitkomstmaat
Maatregel Beschrijving
Tijdsspanne
Whole-body carbohydrate oxidation
Tijdsspanne: 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.
During the 90-minute exercise bout
Whole-body fat oxidation
Tijdsspanne: 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.
During the 90-min exercise bout
Exogenous glucose oxidation
Tijdsspanne: 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.
During the 90-min exercise bout
Exogenous leucine oxidation
Tijdsspanne: 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.
During the 90-min exercise bout

Secundaire uitkomstmaten

Uitkomstmaat
Maatregel Beschrijving
Tijdsspanne
Time to task failure
Tijdsspanne: Immediately following the 90-min exercise bout

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.
Immediately following the 90-min exercise bout

Medewerkers en onderzoekers

Hier vindt u mensen en organisaties die betrokken zijn bij dit onderzoek.

Sponsor

University of Toronto

Onderzoekers

  • Hoofdonderzoeker: Jenna Gillen, PhD, University of Toronto

Studie record data

Deze datums volgen de voortgang van het onderzoeksdossier en de samenvatting van de ingediende resultaten bij ClinicalTrials.gov. Studieverslagen en gerapporteerde resultaten worden beoordeeld door de National Library of Medicine (NLM) om er zeker van te zijn dat ze voldoen aan specifieke kwaliteitscontrolenormen voordat ze op de openbare website worden geplaatst.

Bestudeer belangrijke data

Studie start (Geschat)

30 september 2026

Primaire voltooiing (Geschat)

30 juni 2027

Studie voltooiing (Geschat)

30 juni 2027

Studieregistratiedata

Eerst ingediend

14 september 2026

Eerst ingediend dat voldeed aan de QC-criteria

14 september 2026

Eerst geplaatst (Werkelijk)

18 september 2026

Updates van studierecords

Laatste update geplaatst (Werkelijk)

18 september 2026

Laatste update ingediend die voldeed aan QC-criteria

14 september 2026

Laatst geverifieerd

1 september 2026

Meer informatie

Termen gerelateerd aan deze studie

Trefwoorden

Aanvullende relevante MeSH-voorwaarden

Andere studie-ID-nummers

  • HSREB50670

Plan Individuele Deelnemersgegevens (IPD)

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NEE

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Bestudeert een door de Amerikaanse FDA gereguleerd geneesmiddel

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Bestudeert een door de Amerikaanse FDA gereguleerd apparaatproduct

Nee

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