Comparing the Effects of a High- and Low-carbohydrate Pre-exercise Meal Relative to Fasting on Exercise Metabolism, Subsequent Appetite, and Energy Intake in Healthy Males.

Brief Summary

Detailed Description

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.

Primary Outcomes

Secondary Outcomes

• Voluntary energy intake (Kilocalories) at a laboratory-based test meal.(60 minutes following the end of the exercise session.)
• Glucagon-like peptide-1 (GLP-1)(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Acylated ghrelin(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Visual Analogue Scale for Subjective Ratings of Appetite.(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Insulin(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Non-esterified fatty-acids (NEFA)(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Pre-exercise Subjective Feelings.(Immediately before the exercise session.)
• Enjoyment of the Exercise Bout.(Immediately following the end of the exercise session.)
• Rate of Energy Expenditure During Steady-State Exercise(Throughout the 60-minute steady-state bout of cycling)
• Peptide tyrosine-tyrosine (PYY)(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Glycerol(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Carbohydrate Oxidation Rate At Rest(Baseline, 1 hour, 1.75 hours, 2.75 hours, 5 hours)
• Fat Oxidation Rate At Rest(Baseline, 1 hour, 1.75 hours, 2.75 hours, 5 hours)
• Rate of Energy Expenditure At Rest(Baseline, 1 hour, 1.75 hours, 2.75 hours, 5 hours)
• Glucose(Baseline, 1 hour, 1.75 hours, 2.75 hours, 3 hours, 3.5 hours (mid-exercise), 4 hours, 5 hours.)
• Carbohydrate Oxidation Rate During Steady-State Exercise(Throughout the 60-minute steady-state bout of cycling)
• Rating of Perceived Exertion (RPE).(Throughout the 60-minute steady-state bout of cycling.)