Effects of Pre-exercise Carbohydrate Restriction Relative to Fasting on Metabolism, Appetite, and Energy Intake in Healthy Males.

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

COMPLETED

Clinical Phase

NA

Total Enrollment

12 participants

Study Classification

INTERVENTIONAL

Study Start Date

2021-09-01

Study Completion Date

2022-06-30

Brief Summary

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This study will compare the metabolic, appetite, energy intake, and perceptual responses to a bout of exercise completed in the evening after after a low-carbohydrate lunch meal (\<10% carbohydrate content / 0.2 g/kg carbohydrate; LO-CHO), with the responses to exercise performed after a lunch meal containing a high carbohydrate content (\~60% carbohydrate content / 2.2 g/kg carbohydrate; HI-CHO), and after skipping lunch and fasting for 8 hours since breakfast (FAST).

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Detailed Description

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Regular exercise is known to be a successful strategy for improving several facets of health and maintaining body weight. However, many people are not engaging in enough exercise, and some may not be achieving maximum benefits from the exercise that they already do. Performing exercise in the overnight fasted state has been shown to reduce energy intake over the course of a single day, without any compensatory reductions in free-living energy expenditure. Despite these promising findings, it is likely that not every member of the population is logistically able to perform exercise in the morning due to various work, family and social commitments, and exercise in the evening may be a logical alternative for these individuals.

Studies have found that exercise performed after an overnight fast may incur superior improvements in insulin sensitivity in lean individuals (Van Proeyen et al., 2010), and individuals with overweight or obesity (Edinburgh et al., 2020), compared to exercising after breakfast. These superior improvements may be mediated, in part, by an increased mobilisation and oxidation of endogenous lipid stores. Additionally, overnight fasted exercise may result in a more negative energy balance than exercising after breakfast (Bachman et al., 2016; Edinburgh et al., 2019). We recently examined whether exercise performed in the evening following an extended period of fasting (7 h) would induce similar responses to overnight fasted exercise regarding substrate oxidation patterns and subsequent energy intake (manuscript in preparation - NCT04742530). This research question was important, as we speculate that a large proportion of the population are likely unable to perform exercise in the morning after an overnight fast due to various logistical barriers. Therefore fasting prior to evening exercise could act as an alternative for these individuals.

We found that compared to consuming a carbohydrate-containing meal 2 h prior, fasting before evening exercise resulted in elevated fat oxidation rates during exercise, but was accompanied by compensatory eating at dinner. Additionally, participants reported that fasting throughout the afternoon was difficult. The long-term efficacy of fasted evening exercise may, therefore, be limited by increased hunger and compensatory energy intake.

Consuming a meal lower in carbohydrate and higher in protein and/or fat can increase rates of fat oxidation during exercise (Rowlands \& Hopkins, 2002; Oliviera et al., 2021). Protein is also the most satiating macronutrient, and high-protein diets are associated with reductions in energy intake. Consuming a high-protein pre-exercise meal compared to a typical high-carbohydrate meal also led to greater exercise-induced elevations in hormones typically associated with increased satiety and reduced hunger: peptide tyrosine-tyrosine (PYY) and glucagon-like peptide-1 (GLP-1) (Oliviera et al., 2021). Therefore, consuming a meal with a low carbohydrate content and higher protein content before exercise, rather than completely fasting, could be utilised to enhance the metabolic responses to exercise, whilst simultaneously managing appetite and subsequent energy intake. Further research is needed to fully understand the metabolic and appetite-related effects of a low-carbohydrate, higher-protein meal prior to exercise in the evening, compared to a typically consumed higher-carbohydrate meal and complete fasting.

Conditions

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Obesity Metabolic Syndrome

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

The study design is a randomised, controlled, crossover design in which participants undertake three exercise conditions in a randomised order with at least a seven day period in between trials.

Primary Study Purpose

BASIC_SCIENCE

Blinding Strategy

SINGLE

Participants

Due to the obvious differences between fasting and consuming food, participants will be aware of when they have been assigned to the fasted condition. However, the low- and high-carbohydrate content lunch meals will be closely matched for taste, with carbohydrate content being manipulated within a drink. Participants will not be informed that the carbohydrate content of the lunch meals is being manipulated, and will therefore, be blinded to this element of the study.

Study Groups

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Low-Carbohydrate Pre-Exercise Meal

Participants will consume a low-carbohydrate (\<10% carbohydrate) lunch meal at 13:30 - 2.5 hours prior to commencing exercise at 16:00.

Group Type EXPERIMENTAL

Low-Carbohydrate Pre-Exercise Meal

Intervention Type BEHAVIORAL

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having consumed a low-carbohydrate lunch meal (\<10% carbohydrate; 35% estimated energy requirements) 2.5 hours prior.

High-Carbohydrate Pre-Exercise Meal

Participants will consume a high-carbohydrate (\~2.2 g/kg carbohydrate) lunch meal at 13:30 - 2.5 hours prior to commencing exercise at 16:00.

Group Type EXPERIMENTAL

High-Carbohydrate Pre-Exercise Meal

Intervention Type BEHAVIORAL

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having consumed a high-carbohydrate lunch meal (\~2.2 g/kg carbohydrate; 35% estimated energy requirements) 2.5 hours prior.

Fasted Exercise

Participants will skip lunch, and continue fasting since breakfast (08:00) before commencing exercise at 16:00. Therefore, exercise will commence after an 8 hour period of fasting.

Group Type EXPERIMENTAL

Fasted Exercise

Intervention Type BEHAVIORAL

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having skipped lunch, and having consumed nothing other than plain water since breakfast (08:00; 25% estimated energy requirements). Exercise will therefore commence after an 8 hour period of fasting.

Interventions

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Low-Carbohydrate Pre-Exercise Meal

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having consumed a low-carbohydrate lunch meal (\<10% carbohydrate; 35% estimated energy requirements) 2.5 hours prior.

Intervention Type BEHAVIORAL

High-Carbohydrate Pre-Exercise Meal

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having consumed a high-carbohydrate lunch meal (\~2.2 g/kg carbohydrate; 35% estimated energy requirements) 2.5 hours prior.

Intervention Type BEHAVIORAL

Fasted Exercise

Sixty minutes of cycling at 60% VO2peak will take place on a stationary bicycle ergometer at 16:00, after having skipped lunch, and having consumed nothing other than plain water since breakfast (08:00; 25% estimated energy requirements). Exercise will therefore commence after an 8 hour period of fasting.

Intervention Type BEHAVIORAL

Eligibility Criteria

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Inclusion Criteria

1. Non-smokers (due to the well-known impact of smoking on appetite.
2. Not currently on a weight management program or have an unusual eating pattern (i.e., extended fasting periods \>8 h other than overnight).
3. Have maintained a stable weight for 6 months (self-reported).
4. No history of gastric, digestive, cardiovascular or renal disease (self-reported).

Exclusion Criteria

1. Severe food allergies, dislike or intolerance of study foods or drinks.
2. Currently undergoing a lifestyle intervention (structured diet or exercise).
3. Diagnosis of a condition or currently undergoing treatment therapy known to affect glucose or lipid metabolism (e.g., type-2 diabetes, taking statins), or contraindications to exercise.
4. Use of medication or supplements that may affect hormone concentrations and/or substrate metabolism.
5. Excessive alcohol consumption (\>14 units/week).
6. Intensive training schedule (\>10 hours/week).

Minimum Eligible Age

18 Years

Maximum Eligible Age

40 Years

Eligible Sex

MALE

Accepts Healthy Volunteers

Yes