Energy bars usually are packed with 200 to 500 calories. Some bars also contain protein or fat. Most are fortified with vitamins and minerals and a few even include herbs. Claims that these bars burn fat, build muscle and decrease your susceptibility to injury are simply unfounded. During exercise, your body derives energy by breaking down carbohydrates and fats.
Carbohydrates require less oxygen to break down for energy than do fats.
Consuming a large dose of carbohydrates before or soon after starting to exercise means a lot of this nutrient enters the blood and is available for use by the muscles. If you choose to use an energy bar, be sure to drink water with it. Usually 12 to 16 ounces are needed. Also, because this mix of high-dose carbohydrates and water may lead to an upset stomach, it is best to first try this approach with a long training bout instead of on race day. If you're interested in eating a high protein bar, reserve this practice for after exercise because little protein is used for energy during exercise.