Since ancient Greece, athletes have been interested in nutrition. Over the centuries, athletes, coaches and scientists have experimented with practically everything imaginable to boost athletic performance. In the past 20 years, scientists have sorted out many of the basics of sports nutrition. If you're not getting enough water, all other aspects of sports nutrition really don't matter. All the purported magic of powders, pills and bars goes down the drain if you're dehydrated.
Most people lose about two quarts of water during an hour of jogging or other similar exercise.
Two quarts of water weigh four pounds. Try weighing yourself before and after exercising. Most of the weight loss is due to water loss. The loss of body fat during an hour of exercise is typically less than one ounce. Research shows that exercise performance starts to decline after we lose about 2 percent of our body weight from sweat production.