Substituting Carbohydrate For Added Protein Increases Fat Oxidation During Early-evening Exercise In Healthy Males

Pre-exercise nutrition mediates the effects of exercise. Fasted-state exercise increases fat oxidation and can improve some markers of metabolic health but is difficult to implement when exercise takes place in the evening. The metabolic effects of fasted exercise can be replicated by restricting pre-exercise carbohydrate intake exclusively, but how meal composition prior to evening exercise effects metabolism, appetite, and post-exercise energy intake is unknown. PURPOSE: This study examined the effects of substituting carbohydrate at lunch for added protein on early-evening exercise metabolism, appetite-regulatory hormones, and subsequent energy intake. METHODS: Twelve healthy males completed three trials in randomized, counterbalanced order. Participants consumed a standardized carbohydrate-rich breakfast (779 ± 66 kcal; ~08:15), before a lunch (1186 ± 140 kcal; ~13:15) containing either 0.2 g·kg-1 carbohydrate (LC), 2 g·kg-1 carbohydrate (HC) or no lunch (FAST). At ~16:15, participants completed 1 h cycling at 60% V̇O2peak. Post-exercise ad-libitum energy intake was measured in the laboratory (~18:30). Substrate oxidation and subjective appetite, along with plasma concentrations of glucose, insulin, non-esterified fatty acids (NEFA), glycerol, peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and acylated ghrelin (AG) were measured serially for 5 h after lunch and analysed as total area-under-the-curve. RESULTS: Fat oxidation (HC: 3.9 ± 1.9; LC: 6.7 ± 1.7; FAST: 6.1 ± 1.0 g) and NEFA concentrations (HC: 0.19 ± 0.06; LC: 0.33 ± 0.11; FAST: 0.61 ± 0.16 mmol·L-1) were lower in HC than LC and FAST, but also lower in LC than FAST (all p < 0.01). Subjective appetite was greater in LC and HC versus FAST (p < 0.001), and in LC versus HC (p < 0.01). PYY and GLP-1 concentrations were greater during LC than HC and FAST (p < 0.01), but also greater in HC versus FAST (p < 0.01). AG concentrations were lower during HC and LC versus FAST (p < 0.01). Ad-libitum energy intake was lower in LC versus FAST (-383 ± 233 kcal; p < 0.001) and HC (-313 ± 284 kcal; p < 0.001) but was not different between HC and FAST (p = 0.194). CONCLUSION: A low-carbohydrate, high-protein lunch increased fat oxidation during early-evening exercise and reduced appetite and subsequent energy intake more than a high-carbohydrate, lower-protein lunch. Supported by: The submitted work received no external funding. I have previously received research funding from Innovate UK, Innate Essence Ltd., Society for Endocrinology and the British Nutrition Foundation.