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% V̇O2peak 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.