I have a book on my pile to read which looks interesting: Waterlogged
Drink to thirst regardless of how much weight you lose. The ACSM guideline that one should not lose more than 2 percent body weight is contrary to the published evidence and the findings in elite athletes that drinking "ahead of thirst" impairs exercise performance.
Can you talk a little bit about the history of dehydration and sports marketing?One of the principles of selling a product, and if it’s a medical product and you make medical claims, is that you must maximize your market. In my view, those 1996 guidelines, what they do is they maximize the markets for sports drinks. What they are essentially saying is that it’s dangerous to lose any weight during exercise. In other words, it doesn’t matter what exercise you’re doing, you must drink at the same rate that you are sweating. And you mustn’t wait to become thirsty. What that means is that if you go to a gym and start exercising for 10 minutes, you must start drinking before you start, and within 10 minutes you must have drunk a certain amount. That increases the market size for your product, from just marathon runners to everyone who exercises. So when you go onto the street and you see runners jogging along for a couple of miles, they are carrying water with them. They become a target user for your product. They managed to change drinking behavior out of competitive sport for runners and cyclists and triathletes to gym exercisers as well. The consequence of that is that the sale of their product just rocketed thereafter. They had to demonize hydration and make it a disease.