When replenishing

By Robert H. Shmerling, M.D.

Driving along the freeway recently, a billboard caught my eye. In bold letters it proclaimed: Milk hydrates better than water. Wait, could this be true? And if so, should I be rehydrating with milk after a workout? And should we all have milk, rather than water, in our water bottles?

Unsurprisingly, the ad is sponsored by the milk industry. And while I’d never heard this claim before, the studies aren’t particularly new or compelling. The website supporting this ad cites three small studies dating back more than a decade.

A 2007 study enrolled 11 volunteers (five men, six women) who exercised until they were markedly dehydrated on several occasions. Each time they rehydrated with a different drink, and their urine output was measured over the following five hours. After drinking milk, the study volunteers produced less urine (and therefore retained more fluid) than with water or a sports drink (Powerade). Therefore, milk was considered to provide better hydration.

A study published in 2016 described seven men with marked dehydration following exercise who drank fat-free milk, water, or Powerade. The results were similar.

A 2016 study enrolled 72 healthy, wellhydrated men who drank various fluids and then had their urine production measured over the next four hours. The drinks used in this study were water, whole milk, skim milk, beer,