When you exercise, do you really have a “deep down body thirst” that only a sports drink like Gatorade can quench? Or are you just buying a mouthful of marketing hype? Sports drinks have proliferated since Gatorade first appeared more than 40 years ago. Nowadays, a multitude of brands—Accelerade, Powerade, GU2O, Cytomax, Vitalyte, LUNA Sport, etc.—each tout themselves as the best sports drink for your exercise needs. Are they really as beneficial as they claim?

HYDRATION STATION  When you exercise, you sweat. When you sweat, your body loses water. If too much water is lost, your performance will be compromised as you become dehydrated. It’s not rocket science: You need to drink enough fluids to replace what you lose to function at your best. In this regard, sports drinks are beneficial simply because they are tastier; you’re more likely to consume sufficient amounts of the stuff, especially if it’s a flavor you like. Or you can just drink enough regular (but taste-deficient) water. Studies indicate there’s little difference between the two in terms of how fast the fluid is absorbed into your body.

ELECTROLYTE HYPE   Sports drinks makers often promote the fact that their products provide crucial electrolytes, such as sodium and potassium, that are sweated out and lost during exercise. “There seems to be a real marketing effort to push the importance of electrolytes,” says Dr. Scott Montain, a research physiologist at the U.S. Army’s Research Institute of Environmental Medicine in Natick, Mass. “But the reality is you need to lose enough before you need to replace them.” And only under certain circumstances does that occur, he explains, such as the profuse and prolonged sweating caused by endurance events like triathlons or ultramarathons, or in hot, high-sweat environments where people have limited access to food (our normal and perfectly adequate electrolyte source) for long periods. “It certainly is a minority of situations,” Montain points out. The upshot? Electrolyte replacement is seldom a concern for most activities.

POWER SURGE   Your body has a limited reserve of readily available energy. During periods of sustained exercise, those reserves need to be replaced for optimal performance. In this regard, sports drinks do provide a marked benefit. Sports drinks contain different blends of simple carbohydrates—glucose, fructose, maltodextrin, and others—that can be quickly absorbed and utilized for energy. Different brands often tout the benefits of their unique carb mixes, but for the most part this is more marketing than science. “Your body can oxidize, or utilize, about 60 grams of carbohydrates per hour, or about one gram per minute,” explains Dr. Sam Cheuvront, another research physiologist at the Natick institute. “You can vary the types of carbohydrate but that number appears to be a pretty fixed value. The reality is that during exercise they all perform the same.”

A GAME OF CONCENTRATION   Most sports drinks have a carbohydrate concentration of between 3 and 8 percent, “a nice compromise between fluid replacement and energy replacement,” Montain notes. At concentrations higher than 8 percent, fluids leave the stomach at a slower rate. For low-sweat activities, this effect on “gastric emptying” is not necessarily a concern. “Say you’re hiking and not sweating that much, but burning a lot of calories,” Montain continues. “You can go to a more concentrated beverage and provide yourself with more energy because the slower gastric emptying is not an issue.” On the other hand, a lower concentration is better for intense, high-sweat activities where you’ll be consuming larger amounts of fluids. To calculate carbohydrate concentration, divide the amount of carbs (in grams) per serving by the amount of fluid in a serving (in milliliters), then multiply by 100.

WORK IT OUT   So which is the best sports drink for you? As a general rule, it’s simply whichever tastes best to you personally. And while carbohydrate concentration may affect your decision to some extent, keep in mind that powdered sports drinks allow you to manipulate this aspect to your preference as you mix them. Plus, for many activities, simple water will serve you just fine. Bottoms up!

Correction: This story originally misstated the number of grams of carbohydrates the human body can oxidize per hour (December 2010).