Nutrient Timing in Connection to Evening Exercise

Impact of Carbohydrate Timing on Glucose Metabolism and Substrate Oxidation Following High-Intensity Evening Aerobic Exercise in Athletes: A Randomized Controlled Study

Physical exercise (PE) significantly influences insulin sensitivity (IS), glucose control and overall metabolic health. While PE effectively enhances IS and glucose regulation, the timing of nutrient intake, before and after exercise, plays a crucial role in modulating its effects.

The aim of this study is to evaluate how pre- or post-evening exercise carbohydrate (CHO) ingestion influences glucose metabolism and substrate oxidation (fat/CHO) during exercise and after exercise in athletes during the nocturnal period and the morning after during an oral glucose tolerance test (OGTT).

Study Overview

• Status: Completed
• Conditions: Blood Glucose; Lipid Metabolism; Oral Glucose Tolerance Test; Carbohydrate Metabolism
• Intervention / Treatment: Other: Carbohydrate timing - carbohydrate intake before or after exercise

Detailed Description

The aim of this study is to evaluate how pre- or post-evening exercise carbohydrate (CHO) ingestion influences glucose metabolism and substrate oxidation (fat/CHO) during exercise and after exercise in athletes during the nocturnal period and the morning after during an oral glucose tolerance test (OGTT).

The primary objective is to assess glucose regulation during a 120-minute OGTT the following day.

The secondary objective is to investigate substrate metabolism (CHO and fat oxidation) during a 120-minute OGTT the following day.

Ten healthy, well-trained male endurance cyclists/triathletes, aged 19-45 years, are recruited via local contacts from the Gothenburg region, Sweden. The study is performed in accordance with the Declaration of Helsinki 2008 and is approved by the Swedish Ethical Review Authority (Dnr: 2022-03056-01). All participants gave their written informed consent before inclusion.

The study has a double-blind, randomized, placebo-controlled, crossover design.

After baseline assessment and determination of maximal oxygen uptake (VO2 max), participants undergo a familiarization cycle exercise trial. This trial serves a dual purpose: first, to establish the appropriate amount of CHO to be incorporated into the pre- or post-drink for subsequent cycle experimental trials, and second, to familiarize participants with the equipment and study protocol.

Three days prior to the cycle experimental trial, subcutaneous insertion of a glucose sensor for continuous glucose monitoring (CGM) takes place. Participants are randomly assigned to consume either a CHO drink or a placebo (PLA) drink (containing no energy) two hours prior to the cycle experimental trial that starts at 19:30. During the exercise trial, participants engage in submaximal cycling exercise at 70% of their maximal workload (Wmax), followed by a 25-minute time trial (TT). The total duration of the exercise session is approximately 90 minutes. Workload during the TT is individualized based on each participant's maximal work capacity (Wmax). During exercise, capillary glucose levels, heart rate, and rate of perceived exertion (RPE; Borg category scale 6-20) are measured. Additionally, respiratory gases are collected during 5-minute periods at every 15-minute interval to assess substrate utilization.

Immediately after completing the TT, participants switch to the opposite drink condition: those who initially received the CHO drink consume the PLA drink, and vice versa. The amount of CHO in the CHO drink consumed by each participant is precisely matched to the amount of CHO that the participant oxidizes during the exercise trial.

After the ingestion of the CHO- or placebo drink, participants fast overnight. CGM technology is used to measure interstitial glucose values during the night.

At 08:00, participants consume a 300mL solution containing 75g glucose for a 120-min OGTT. Capillary blood samples are collected at baseline and every 15 minutes during the OGTT. Respiratory gases are collected to measure substrate oxidation. The same protocol is reproduced the following week, with the reverse order of the test drink intake.

Three days preceding both control and experimental trials, participants are provided with a standardized diet consisting of pre-packaged meals that match their daily energy and macronutrient needs to prevent energy deficiency.

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Sweden
  • Bohuslän
    • Göteborg, Bohuslän, Sweden, 405 30
      • Department of Food and Nutrition, and Sport Science, Centre for Health and Performance, University of Gothenburg, Gothenburg, Sweden

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Females and males
• 18-50 years
• Endurance fitness level of ≥40 mL O2/kg/min.
• Signed informed consent

Exclusion Criteria:

• Medical treatment and/or nutritional supplements that may affect glucose tolerance, substrate oxidation and performance capacity

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Carbohydrate drink; All study participants will receive the carbohydrate (CHO) drink and the placebo in a randomized, doubleblind crossover fashion. The CHO drink and placebo products have similar appearance and taste.	Other: Carbohydrate timing - carbohydrate intake before or after exercise; The study aims to investigate how pre- or post evening exercise carbohydrate ingestion influences glucose metabolism and substrate oxidation (fat/CHO) during exercise and after exercise in athletes during the nocturnal period (21:00-06:00) and the morning after during an 120 minute oral glucose tolerance test (OGTT).
Placebo Comparator: Placebo; All study participants will receive the carbohydrate (CHO) drink and the placebo in a randomized, double-blind crossover fashion. The CHO drink and placebo products have similar appearance and taste.	Other: Carbohydrate timing - carbohydrate intake before or after exercise; The study aims to investigate how pre- or post evening exercise carbohydrate ingestion influences glucose metabolism and substrate oxidation (fat/CHO) during exercise and after exercise in athletes during the nocturnal period (21:00-06:00) and the morning after during an 120 minute oral glucose tolerance test (OGTT).

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
To investigate change in glucose tolerance during a 75g glucose, 120 min oral glucose tolerance test (OGTT)	To quantify participants' glucose tolerance, the change in plasma glucose levels (mmol/L) will be measured over a 120-minute period following the ingestion of a standardized 75g glucose solution during an OGTT.	Comparing the change in glucose tolerance during the OGTT between baseline (no exercise) week 0, compared to interventions week 1 and week 2 involving previous evening exercise, with carbohydrates consumed either before or after exercise.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
To investigate substrate oxidation during the oral glucose tolerance test (OGTT)	To quantify substrate oxidation rates (carbohydrate oxidation (g/minute) and fat oxidation (g/minute), the change in respiratory exchange ratios (RER) will be measured during the 120-minute OGTT period.	Comparing the change in substrate oxidation during the OGTT between baseline (no exercise) week 0, compared to interventions week 1 and week 2 involving previous evening exercise with carbohydrates being consumed either before or after exercise.

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
To investigate performance capacity during a cycle ergometer time trial (TT).	Performance capacity was assessed by measuring the time (seconds) required to complete a specific amount of work.	Comparing the change in performance capacity between the interventions involving carbohydrates being consumed either before (week 1) or after the time trial (week 2). Note that respective arm will be randomized.
To investigate substrate oxidation during 50 min submaximal evening exercise.	To quantify substrate oxidation rates (carbohydrate oxidation (g/minute) and fat oxidation (g/minute), the change in respiratory exchange ratios will be measured during the 50 min submaximal exercise.	Comparing the change in substrate oxidation between the interventions involving previous evening exercise with carbohydrates being consumed either before (week 1) or after exercise (week 2). Note that respective arm will be randomized.
To investigate nocturnal glucose regulation.	To quantify participants' nocturnal glucose regulation, the change in interstitial glucose levels (mmol/L) will be measured during the period 21:00-06:00 utilizing continuous glucose monitoring (CGM).	Comparing the change in glucose levels (mmol/L) during the period 21:00-06:00 between baseline (no exercise) week 0, compared to interventions week 1 and week 2 involving previous evening exercise, with CHO consumed either before or after exercise.

Collaborators and Investigators

• Sponsor: Göteborg University
• Collaborators: Örebro University, Sweden
• Investigators: Principal Investigator: Stefan Pettersson, Assoc. Prof., Department of Food and Nutrition, and Sport Science, University of Gothenburg, Sweden

Study record dates

Study Major Dates

• Study Start (Actual): January 10, 2022
• Primary Completion (Actual): September 2, 2022
• Study Completion (Actual): September 2, 2022

Study Registration Dates

• First Submitted: April 11, 2024
• First Submitted That Met QC Criteria: May 3, 2024
• First Posted (Actual): May 6, 2024

Study Record Updates

• Last Update Posted (Actual): May 6, 2024
• Last Update Submitted That Met QC Criteria: May 3, 2024
• Last Verified: May 1, 2024

More Information

Terms related to this study

• Keywords: Exercise; Nutrition; Continuous glucose monitoring; Metabolism; Athletes
• Other Study ID Numbers: Dnr: 2022-03056-01

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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