Since excess storage fat develops when intake of the food required to produce energy exceeds the amount of energy used in metabolism and in physical activity, the treatment of excess fat must alter one or both aspects of the energy stream. The options are to decrease energy intake or to increase energy output, or both. Storage fat is meant to protect its bearer from starvation when food is unavailable, and before fat is tapped for energy. In the face of decreased intake of food, the body breaks down muscle to construct the sugar it needs to feed the brain. Much of the early weight loss on a very low calorie diet represents loss of muscle tissue rather than loss of fat, which is not good. Similarly, fat is not easy to access as fuel for exercise. A person of normal weight has enough body fat to fuel the muscles for days of continuous running, but will collapse long before burning any significant amount fat stored by the body. Along with weight loss or dieting programs, the subject also has to change the attitude to eating.