0903 Milk as a post-exercise rehydration fluid

Paediatricians are partly ‘programmed’ to avoid milk as a rehydration fluid. This is probably because for the most part dehydration occurs in infants and is associated with confounders such as infection and lactose intolerance. It is nevertheless quite interesting to see sports and exercise scientists begin to study and write about skim milk as an alternative to commercial rehydration drinks, as referenced in an insert placed by Milk SA’s Consumer Education Project in a recent issue of the South African Medical Journal. This may well be of relevance to paediatricians who advise sports-active adolescents on appropriate diet, and if that is the case then it is useful to also know about some of the current issues in the field. Noakes, well-known internationally for his pioneering work in exercise science and sports medicine, has for some years been concerned about overhydration and hypontraemia in some endurance athletes who have followed advice of international bodies and sports drink manufacturers. This advice, which was typically been along the lines of drinking “as much as tolerable,” is now being tempered, substantially as a result of Noakes’ studies of overhydrated Comrades Marathon athletes who have collapsed around race-end and been shown to be significantly hyponatraemic. Rehydration fluids have to date contained differing concentrations of carbohydrate and electrolytes, but protein has not been part of the mix. Noting that milk contains both of these ingredients in a quality protein “natural matrix” there have been several studies comparing post-exercise rehydration with milk vs carbohydrate-electrolyte drinks. Reports have been that milk-rehydration results in positive fluid balance whereas the sports drinks are associated with ‘euhydration’ or negative balance. It is uncertain whether the studies to date meet Noakes’ requirement to not promote a modality or guideline until it has been subjected to rigourous study and analysis, and perhaps more information is required on the specific circumstances in which milk is appropriate (after resistance/weight training vs after endurance exercise vs during an event such as the Comrades).

Read more:
S Afr J Med 2009; 99: 17
Br J Nutr 2008; 104: 633-42
Br J Sports Med 2008; 42: 496-501
J Sports Sci 2007; 25: 781-96