Effect of milk protein addition to a carbohydrate–electrolyte rehydration solution ingested after exercise in the heat

Abstract

The present study examined the effects of milk protein on rehydration after exercise in the heat, via the comparison of energy- and electrolyte content-matched carbohydrate and carbohydrate-milk protein solutions. Eight male subjects lost 1·9 (SD 0·2) % of their body mass by intermittent exercise in the heat and rehydrated with 150% of their body mass loss with either a 65 g/l carbohydrate solution (trial C) or a 40 g/l carbohydrate, 25 g/l milk protein solution (trial CP). Urine samples were collected before and after exercise and for 4 h after rehydration. Total cumulative urine output after rehydration was greater for trial C (1212 (SD 310) ml) than for trial CP (931 (SD 254) ml) (P < 0·05), and total fluid retention over the study was greater after ingestion of drink CP (55 (SD 12) %) than that after ingestion of drink C (43 (SD 15) %) (P < 0·05). At the end of the study period, whole body net fluid balance (P < 0·05) was less negative for trial CP (-0·26 (SD 0·27) litres) than for trial C (-0·52 (SD 0·30) litres), and although net negative for both the trials, it was only significantly negative after ingestion of drink C (P < 0·05). The results of the present study suggest that when matched for energy density and fat content, as well as for Na and K concentration, and when ingested after exercise-induced dehydration, a carbohydrate-milk protein solution is better retained than a carbohydrate solution. These results suggest that gram-for-gram, milk protein is more effective at augmenting fluid retention than carbohydrate.