Energy is something all creatures need and something Americans apparently believe they are in terribly short supply of, as exhibited by the amazing profusion of flavored waters containing antioxidants, electrolytes, vitamins, and shots of caffeine. These drinks—and the ingredients within—can be broken down into a few basic categories.
THE CALORIE QUESTION
To provide actual bona fide energy, a drink has to contain calories, and that usually means sugar. If you're concerned about calories—and if that's one reason you're on the treadmill at the gym in the first place—read the labels.
First, check serving size.Some beverages have 2 to 3 servings per bottle or can, so if your drink is not calorie-free, serving size is important. Calories in energy drinks most often come from sugar: 4 calories per gram. A 12-ounce Coke, for reference, has 140 calories.
Second, ask if these are the right kind of calories.The body perceives calories delivered in liquid form as less physiologically satisfying than those found in solid foods. It may be better to drink a noncaloric drink and eat a fiber-rich energy bar.
Caffeine is the key ingredient, sometimes from ingredients such as guarana, cacao, or mate. Not an energy source per se, but a nervous-system stimulant that does provide a short-term boost. If the amount of caffeine is listed, here's a reference: An 8-ounce cup of coffee has about 150mg.
"Electrolytes" is the umbrella term for minerals like sodium, potassium, and chloride that assist in cellular function and regulate fluid balance—life-saving in cases of severe fluid loss. They are also lost through sweat during exercise, but unless you're an endurance athlete, tap water and a balanced diet will supply all you need, even after a 45-minute Spin class. These come in caloric and noncaloric versions.
The Bs are crucial for metabolism—the process by which the body breaks down food and uses it for energy. But you likely get all the Bs you need from a balanced diet, and their ability to provide an energy boost in beverage form is unproven.
From vitamin C to resveratrol, there are thousands of antioxidants so far known to science that are involved in the prevention of cellular damage. They exist in complex combinations in whole foods and drinks closely derived from them (like tea or juice). Problem is, there's little evidence showing that isolating these compounds in a drink has an effect on immunity.