Protein added to a sports drink improves fluid retention.

The purpose of this study was to compare fluid retention of carbohydrate plus protein, a carbohydrate-only, and water following 2.5% body weight (BW) loss. Thirteen subjects dehydrated to 2.5% of BW, then ingested a CHO (6%) plus protein drink (1.5%; CP), a 6% CHO drink, or water (WA) at a volume equal to BW loss during a 3-h recovery. Fluid retention was significantly greater for CP (88 +/- 4.7%) than CHO (75 +/- 14.6%), which was greater than WA (53 +/- 16.1%). Serum and urine osmolalities were greater for CP (284.7 +/- 5.0; 569.4 +/- 291.4 mOsm/kg) than CHO (282.6 +/- 5.2; 472.9 +/- 291.5 mOsm/kg) which were greater than WA (280.6 +/- 5.9, 303.7 +/- 251.5 mOsm/kg). Results indicate that fluid retention for CP was 15% greater than CHO and 40% greater than WA. Water ingestion led to a dilution of the serum and resulted in only 53% fluid retention.