One of my favorite books on running is The Runner’s Body by Ross Tucker, PhD and Jonathan Dugas, PhD. What I enjoy so much about this book is the science based approach to exercise and running. The authors dispel many of the so called ‘truisms” of running and fitness training. A good example is the topic of sodium replacement during exercise. Can you drink enough of an electrolyte sports drink during a workout out to replenish the sodium that you lose during sweating? Do we even have to replace it? When we exercise our body temperatures go up. We sweat in order to help regulate the temperature and not allow overheating. Sweat is composed of primarily water and salt with the former being the overwhelming component. The more fit a person becomes the more efficient the sweating and the lower the concentration of sodium of the fluid. When we workout, the blood sodium level does not go down but instead goes up. This is because we lose considerably more water than salt in the sweat. Sports drinks contain too little salt to counteract the effects of sweating on the blood’s electrolyte concentration and therefore, can result in a drop in blood sodium level.

Blood contains 1.4 grams of salt per liter, while some of the best selling sports drinks have only 0.4 grams per liter. This is more dilute than our blood. So, if you consume a lot of a sports drink during a workout, your will actually dilute the blood. Don’t sports drink advertisements tell us that replacing salt is necessary during a workout or performance will suffer? In reality, you cannot elevate your sodium levels by drinking one of these products.

Are sports drinks a better alternative than water? Yes, from the perspective that your blood salt level will not drop as much as water because you are consuming a small amount of sodium. This is however, relative, as it will still drop if you try to drink as much as you can during the workout.

The best advice from the authors is not to overdrink and to listen to your thirst. 

Ross Tucker, PhD and Jonathan Tucker, PhD have a fascinating and very educational blog called The Science of Sports. If you are into the science of all things exercise you will love it.