Substituting Carbohydrate at Lunch for Added Protein Increases Fat Oxidation During Subsequent Exercise in Healthy Males

Context: How pre-exercise meal composition influences metabolic and health responses to exercise later in the day is currently unclear. Objective: Examine the effects of substituting carbohydrate for protein at lunch on subsequent exercise metabolism, appetite, and energy intake. Methods: Twelve healthy males completed 3 trials in randomized, counterbalanced order. Following a standardized breakfast (779 ± 66 kcal; ∼08:15), participants consumed a lunch (1186 ± 140 kcal; ∼13:15) containing either 0.2 g·kg ^-1 carbohydrate and ∼2 g·kg ^-1 protein (LO-CARB), or 2 g·kg ^-1 carbohydrate and ∼0.4 g·kg ^-1 protein (HI-CARB), or they fasted (FAST). Participants later cycled at ∼60% V˙O _2peak for 1 hour (∼16:15) and post-exercise ad libitum energy intake was measured (∼18:30). Substrate oxidation, subjective appetite, and plasma concentrations of glucose, insulin, nonesterified fatty acids (NEFA), peptide YY (PYY), glucagon-like peptide 1 (GLP-1), and acylated ghrelin were measured for 5 hours post-lunch. Results: Fat oxidation was greater during FAST (+11.66 ± 6.63 g) and LO-CARB (+8.00 ± 3.83 g) than HI-CARB (P <. 001), with FAST greater than LO-CARB (+3.67 ± 5.07 g; P <. 05). NEFA were lowest in HI-CARB and highest in FAST, with insulin demonstrating the inverse response (all P <. 01). PYY and GLP-1 demonstrated a stepwise pattern, with LO-CARB greatest and FAST lowest (all P <. 01). Acylated ghrelin was lower during HI-CARB and LO-CARB vs FAST (P <. 01). Energy intake in LO-CARB was lower than FAST (-383 ± 233 kcal; P <. 001) and HI-CARB (-313 ± 284 kcal; P <. 001). Conclusion: Substituting carbohydrate for protein in a pre-exercise lunch increased fat oxidation, suppressed subjective and hormonal appetite, and reduced post-exercise energy intake.