The term fasting refers to voluntarily or involuntarily going without food. A person may fast voluntarily because of an eating disorder, as a dietary practice related to religious proscriptions, or for health reasons, such as weight loss or internal cleansing. There are, however, no nutritional benefits to fasting.
During a full fast a person abstains from all foods except water or other liquids. A person may also engage in a partial fast, during which particular foods are avoided. Extended fasts lasting longer than a few days can be dangerous because intake is not supporting growth and maintenance. Fasting also promotes the development of ketones, which can be harmful to body organs if they accumulate in the body. Ketones are acidic compounds produced from the incomplete breakdown of fats when there is insufficient carbohydrate intake, and they can disturb the body's acid-base balance.
Judith C. Rodriguez
Anderson, J., and Deskins, B. (1995). The Nutrition Bible. New York: William Morrow.