Glycaemic Responses to a Food Intake Sequence Intervention in Free-living Elite Female Athletes

Glycaemic Responses to a Food Intake Sequence Intervention Under Free-living Conditions in Elite Female Athletes

The goal of this clinical trial is to investigate the impact of a food intake sequence intervention under free-living conditions on glycaemic responses in elite female athletes. Specifically, the main questions it aims to answer are:

1. Does consuming breakfast in different food intake sequences alter postprandial interstitial glucose responses?
2. Does consuming a pre-exercise meal in different food intake sequences alter interstitial glucose responses during exercise?
3. Does consuming the last meal of the day in different food intake sequences alter nocturnal interstitial glucose responses?

To address these questions, researchers will compare eating the dietary sources of rapidly absorbed carbohydrate (CHO) at the end (CHO-last meal pattern) or at the start (CHO-first meal pattern) of standardised mixed meals, at different times of day, in a randomised, counterbalanced, crossover design.

Participants will wear a blinded continuous glucose monitor (CGM) for 6 consecutive days during a training camp. Throughout the study, they will be provided with buffet meals, at the same time and location each day. Dietary intake will be ad libitum, except for breakfast and supper, for which participants will select a preferred composition (ingredients, preparation methods, portion sizes) to replicate across study days. In all ad libitum meals (i.e., lunch, snacks, and dinner), they will be asked to maintain their assigned food intake sequence.

• On day 1, athletes will eat freely. An educational session on the study protocol and food sequence manipulation will be delivered, and informed consent, questionnaires, screening assessments, and CGM fitting will be completed. Data collected by the CGM during the first 24 hours will be disregarded due to sensor stabilisation. Hence, this period will serve for familiarisation only.
• On days 2 and 3, one group will eat the last meal of the day (i.e., supper) in a CHO-last meal pattern, while the other will follow a CHO-first meal pattern; on days 3 and 4 one group will eat breakfast in a CHO-last meal pattern while the other will follow a CHO-first meal pattern.
• On days 4 and 5 (supper) and 5 and 6 (breakfast), participants in each group will adhere to the alternate condition.

Concurrent data on potential confounding factors (e.g., dietary intake, physical activity, internal and external load during training sessions/competition, sleep quantity and quality, menstrual cycle phase/status) will be collected.

Due to the short camp duration, implementing a one-day washout period will not be feasible. Therefore, repeated measurements over two consecutive days per condition will be obtained to minimise carryover effects of the food intake sequence from prior meals on end-of-intervention data (the final 24 hours per condition), and to assess intraindividual consistency of outcomes at matched-times and standardised settings.

Glycaemic responses will be compared within-participant between food intake sequences using linear mixed models with random intercepts, to account for repeated measures, interindividual variability, and potential missing data.

Study Overview

• Status: Completed
• Conditions: Healthy; Sleep; Exercise; Dietary Intervention; Nutrition; Glycemic Variability
• Intervention / Treatment: Other: Carbohydrate-last meal pattern; Other: Carbohydrate-first meal pattern

• Study Type: Interventional
• Enrollment (Actual): 22
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Portugal
  • Lisbon District
    • Oeiras, Lisbon District, Portugal, 1495-433
      • Cidade do Futebol

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Adult (18-64 years old)
• Women
• Elite athletes (meeting training and performance caliber criteria ≥Tier 4; McKay et al., 2022)
• Healthy (meeting the exclusion criteria for medical conditions)
• Normal glucose tolerant according to the latest review standards of the American Diabetes Association (ElSayed et al., 2024): HbA1c <5.7%, fasting plasma glucose <5.6 mmol/L (100 mg/dL), or 2-h plasma glucose <7.8 mmol/L (140 mg/dL) during a 75-g OGTT
• Able and willing to provide informed consent and safely comply with study procedures

Exclusion Criteria:

• Any medical condition or behaviour deemed either to pose undue personal risk to the participant or introduce bias into the experiment (e.g. pregnancy, alcohol or substance abuse; any condition affecting the glucose and lipid metabolism or appetite, reviewed on a case by case basis)
• Any reported medication or supplementation that may interfere with the glucose metabolism (e.g., acarbose, aspirin, berberine, insulin, metformin, semaglutide, sulfonylureas, thiazide diuretics, thiazolidinediones, vitamin C). Other medication and supplementation will be reviewed on a case by case basis.
• Recent change in body mass (± 2 kg in the last 2 months)
• Smoking

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: CL - CF; The interventions (carbohydrate-last meal pattern (CL) or carbohydrate-first meal pattern (CF)) will be delivered in random order. If participants are allocated to this study arm, they will receive the CL on the first 2 days and the CF on the next 2 days of the study period.	Other: Carbohydrate-last meal pattern; Participants will consume the main dietary sources of protein, fat, fibre and/or polyphenols before the main dietary sources of simple carbohydrate in the standardised test-meals (breakfast and supper) and will be encouraged to maintain this food intake sequence in the remaining meals of the day. Participants will be instructed to consume lunch and dinner within 30 min, and breakfast and supper within 15 min at a comfortable pace, without intervals between the carbohydrate and non-carbohydrate-rich meal components.; Other Names: CL; CHO-last; Other: Carbohydrate-first meal pattern; Participants will consume the main dietary sources of protein, fat, fibre and/or polyphenols after the main dietary sources of simple carbohydrate in the standardised test-meals (breakfast and supper) and will be encouraged to maintain this food intake sequence in the remaining meals of the day. Participants will be instructed to consume lunch and dinner within 30 min, and breakfast and supper within 15 min at a comfortable pace, without intervals between the carbohydrate and non-carbohydrate-rich meal components.; Other Names: CF; CHO-first
Active Comparator: CF - CL; The interventions (carbohydrate-last meal pattern (CL) or carbohydrate-first meal pattern (CF)) will be delivered in random order. If participants are allocated to this study arm, they will receive the CF on the first 2 days and the CL on the next 2 days of the study period.	Other: Carbohydrate-last meal pattern; Participants will consume the main dietary sources of protein, fat, fibre and/or polyphenols before the main dietary sources of simple carbohydrate in the standardised test-meals (breakfast and supper) and will be encouraged to maintain this food intake sequence in the remaining meals of the day. Participants will be instructed to consume lunch and dinner within 30 min, and breakfast and supper within 15 min at a comfortable pace, without intervals between the carbohydrate and non-carbohydrate-rich meal components.; Other Names: CL; CHO-last; Other: Carbohydrate-first meal pattern; Participants will consume the main dietary sources of protein, fat, fibre and/or polyphenols after the main dietary sources of simple carbohydrate in the standardised test-meals (breakfast and supper) and will be encouraged to maintain this food intake sequence in the remaining meals of the day. Participants will be instructed to consume lunch and dinner within 30 min, and breakfast and supper within 15 min at a comfortable pace, without intervals between the carbohydrate and non-carbohydrate-rich meal components.; Other Names: CF; CHO-first

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incremental interstitial glucose peak after a standardised test meal	Difference between CHO-last and CHO-first meal patterns in the incremental interstitial glucose peak (mmol/L) adjusted for baseline, following standardised breakfasts (independent of and coinciding with subsequent exercise) and the end-of-intervention (days 3 and 5) standardised supper, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	0-120 minutes following a standardised test meal

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incremental area under the interstitial glucose curve after a standardised test meal	Difference between CHO-last and CHO-first meal patterns in the incremental area under the interstitial glucose curve (mmol/L x min) adjusted for baseline, following standardised breakfasts (independent of and coinciding with subsequent exercise) and the end-of-intervention (days 3 and 5) standardised supper, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	0-120 minutes following a standardised test meal
Time-to-peak interstitial glucose after a standardised test meal	Difference between CHO-last and CHO-first meal patterns in the time-to-peak interstitial glucose (minutes), following standardised breakfasts (independent of and coinciding with subsequent exercise) and the end-of-intervention (days 3 and 5) standardised supper, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	0-120 minutes following a standardised test meal
Time out of interstitial glucose range after a standardised test meal	Difference between CHO-last and CHO-first meal patterns in the time spent >7.8 mmol/L and time <3.9 mmol/L (%), following standardised breakfasts (independent of and coinciding with subsequent exercise) and the end-of-intervention (days 3 and 5) standardised supper, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	0-180 minutes following a standardised test meal
Interstitial glucose dip after a standardised test meal	Difference between CHO-last and CHO-first meal patterns in the 2-3-hour interstitial glucose dip (mmol/L), following standardised breakfasts not coinciding with subsequent exercise, and the end-of-intervention (days 3 and 5) standardised supper, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	0-180 minutes following a standardised test meal
Interstitial glucose concentrations during specific activities	Difference between CHO-last and CHO-first meal patterns in the mean interstitial glucose concentrations (mmol/L) across 15-minute averages and adjusted for baseline where relevant, during the following periods: after standardised breakfasts (independent of and coinciding with exercise); after the end-of-intervention (days 3 and 5) standardised supper, during exercise not coinciding with postprandial periods, during evening sleep, and during daytime rest, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	24 hours
Within-day standard deviation of interstitial glucose	Difference between CHO-last and CHO-first meal patterns in the 24-hour standard deviation (SD) of interstitial glucose concentrations during the end-of-intervention monitoring period (days 3 and 5), assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ sensor).	24 hours
Within-day coefficient of variation of interstitial glucose	Difference between CHO-last and CHO-first meal patterns in the 24-hour coefficient of variation (%) of interstitial glucose concentrations during the end-of-intervention monitoring period (days 3 and 5), assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ sensor).	24 hours
Mean amplitude of glycaemic excursions (MAGE)	Difference between CHO-last and CHO-first meal patterns in the mean amplitude of glycaemic excursions (MAGE) during the end-of-intervention monitoring period (days 3 and 5), assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ sensor).	24 hours
Large amplitude of glycaemic excursions (LAGE)	Difference between CHO-last and CHO-first meal patterns in the large amplitude of glycaemic excursions (LAGE) during the end-of-intervention monitoring period (days 3 and 5), assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ sensor).	24 hours
Within-day time out of interstitial glucose range	Difference between CHO-last and CHO-first meal patterns in the time spent >7.8 mmol/L and <3.9 mmol/L (%) over 24 hours during the end-of-intervention monitoring period (days 3 and 5), assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ sensor).	24 hours
Between-day glycaemic variability	Difference between CHO-last and CHO-first meal patterns in the mean of daily differences (MODD) of interstitial glucose responses at matched clock times, assessed using a blinded continuous glucose monitoring system (Freestyle Libre Pro IQ).	24 hours

Collaborators and Investigators

• Sponsor: Universidade do Porto
• Collaborators: Fundação para a Ciência e a Tecnologia; Federação Portuguesa de Futebol
• Investigators: Principal Investigator: Rita Giro, Faculty of Nutrition and Food Sciences of the University of Porto (FCNAUP); FPF Academy, Federação Portuguesa de Futebol

Study record dates

Study Major Dates

• Study Start (Actual): November 24, 2025
• Primary Completion (Actual): November 29, 2025
• Study Completion (Actual): November 29, 2025

Study Registration Dates

• First Submitted: November 14, 2025
• First Submitted That Met QC Criteria: November 21, 2025
• First Posted (Estimated): November 25, 2025

Study Record Updates

• Last Update Posted (Actual): December 5, 2025
• Last Update Submitted That Met QC Criteria: December 4, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: glycaemia; food order; meal sequence; sport nutrition
• Additional Relevant MeSH Terms: Behavior; Motor Activity
• Other Study ID Numbers: FOODSEQ-GRFA; 2022.12954.BD (Other Grant/Funding Number: Fundação para a Ciência e Tecnologia)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Anonymised IPD will be made available upon reasonable request directed to the corresponding author.
• IPD Sharing Time Frame: IPD will become accessible following the publication of all study findings.
• IPD Sharing Access Criteria: IPD will be made available to researchers with legitimate scientific purposes (such as systematic reviews or meta-analyses).
• IPD Sharing Supporting Information Type: SAP; ICF

Drug and device information, study documents

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