The Addition of Protein to a Carbohydrate Supplement Enhances Fluid Retention But Not Running Performance

INTRODUCTION: It is unclear whether or not the isocaloric addition of protein (PRO) to a carbohydrate (CHO) endurance exercise supplement improves exercise performance, recovery, and/or fluid retention. PURPOSE: 1) to determine if a PRO+CHO beverage during and/or after endurance exercise improves performance in a subsequent exercise bout compared to CHO alone, 2) to measure fluid retention as a possible mechanism for enhanced performance. METHODS: Using a randomized crossover design, nine endurance trained subjects (age=33+ or -4.2 yrs; VO sub(2)max=65.1+ or -1.47 ml/kg/min, body fat=7.9+ or -1.0%) received a beverage containing CHO (0.65g of CHO/kg) or CHO + PRO (0.52g of CHO/kg plus 0.13g of protein/kg) during a one hour run at 68% of VO sub(2)max. During a 7 hour recovery period subjects then received beverages containing either CHO (1.0g of CHO/kg) or CHO+PRO (0.80g of CHO/kg plus 0.20g of protein/kg) immediately post-exercise, at 1 and 4 hours of recovery. Urine volume and body weight were measured post-exercise, during recovery at hours 3, 5, and 7 to calculate fluid retention. Subjects then ran a 10-km time trial. RESULTS: There were no statistical differences in 10-km running times or measures of blood glucose or insulin during or after exercise among the four nutritional conditions. However fluid retention was significantly higher at hour 5 of recovery in both conditions in which CHO+PRO (37.2+ or -18.0% and 34.9+ or -19.3%) was provided during recovery as compared to those in which CHO alone (19.7+ or -18.0%) was given. CONCLUSION: While a 4:1 ratio of CHO:PRO provided in recovery may enhance fluid retention compared to CHO alone, this did not lead to improved 10-km running performance.