Whether you exercise for one hour three times a week or run in marathons, your body needs to replenish fluids and sugars. Sports drinks provide carbohydrates and electrolytes that help maintain blood sugar and mineral levels. (See Understanding Sports Drinks to Choose the Right One for You.)

But before you choose a sports drink, you should know what they contain and how your body uses them. Here are some things to think about.

Consider water

The sugar content in some electrolyte-replenishing drinks can add an extra 150 calories. If your exercise session lasts less than 45 to 60 minutes and you are trying to shed a few pounds, water may be a better choice than a drink that contains sugar.

Read labels

Although many sports drinks contain minerals and carbohydrates, not all are beneficial. Look for drinks that contain around 5% carbohydrates—including 3% of the complex carbohydrate maltodextrin and 2% of the simple carbohydrate fructose. The drink should also contain the electrolytes potassium, sodium, magnesium, and calcium. (See Sports Drinks for Athletes: the Good, the Bad, and the Ugly.)

Drink in moderation

Let thirst be your guide for replenishing fluids. If you exercise more than 60 minutes at a time, drink when you feel thirsty, and try to stay within 1 1/2 to 3 1/2 cups of liquid per hour. That’s enough to keep you hydrated when you’re sweating. (See also Hydration for Successful Sports Performance.) If you notice weight gain when you step on the scale immediately after a workout, you should decrease your fluid intake.

Trust your body to let you know when it needs more fluids, and choose a drink that contains a healthy amount of sugars and minerals.