Varying Postprandial, Postexercise Nutrient Timing: Effects On Substrate Oxidation And Protein Retention In Resistance-trained Men

Abstract

Dietary protein and/or carbohydrate consumption augments postexercise recovery by facilitating the rebuilding of damaged contractile tissues and restoring energy reserves, particularly in a postabsorptive state. It is unclear how altering postexercise nutrient timing when in a postprandial state affects the shift towards fat utilization and changes in net protein retention after a resistance training bout. PURPOSE: To examine the effects of immediate versus delayed postexercise nutrient intake on substrate oxidation and protein retention during recovery. METHODS: In a single-blinded, crossover design, resistance trained (≥1 y) men (n=10, 22±2 y, 83±10 kg) consumed a mixed, eucaloric meal 2 hours before performing resistance exercise (3 sets of 6 whole body exercises, 2-3 minutes rest). Participants then consumed one of three postexercise beverages: immediate consumption of a whey protein concentrate (0.35 g/kg) and dextrose (1.0 g/kg) beverage (IMM), delayed consumption (2 h) of a whey and dextrose beverage (+2H), or placebo (flavoring with water) (PLA). Participants recovered (3 h) while expired carbon dioxide and oxygen were analyzed. Carbohydrate and fat oxidation was determined and body protein breakdown was investigated via analyses of salivary cortisol and urinary nitrogen excretion. RESULTS: Nitrogen balance in PLA (-0.02±0.01 g) was significantly lower than +2H (5.21±0.63 g, p=<0.001, ES=11.61) and IMM (5.21±0.64 g) (p=<0.001, ES=11.59) during the three-hour recovery. There were no significant differences in nitrogen balance between IMM and +2H (p=1.0). Carbohydrate oxidation in IMM was significantly higher than +2H at 60 minutes postexercise (0.21±0.13 g/min vs. 0.11±0.12 g/min, respectively; p=0.014). Fat oxidation was higher in +2H than IMM at minute 90 (p>0.05, ES=0.60), minute 120 (p>0.05, ES=0.40), and minute 150 (p>0.05, ES=0.50). There were no significant differences in salivary cortisol among groups (all p=1.0). CONCLUSION: In the postprandial state, +2H promoted higher fat utilization than IMM, whereas IMM promoted greater carbohydrate oxidation earlier in the recovery period. Both interventions resulted in similar net protein retention. Thus, postponing postexercise nutrient intake when in a postprandial state may be implicated in body composition improvements.