For many philosophers, scientists, and physicians, fasting was an essential part of life, health, and the healing process needed to recreate health where there was sickness. Socrates, Plato, Aristotle, Galen, Paracelsus, and Hippocrates all used and believed in fasting therapy. Most spiritual teachers also recommend fasting as a useful tool. In a booklet from the 1947 lecture entitled Healing by God's Unlimited Power, Paramahansa Yogananda suggested that fasting is a way to increase our natural resistance to disease, stating that Fasting is a natural method of healing. When animals or savages are sick, they fast. He continued, Most diseases can be cured by judicious fasting. Unless one has a weak heart, regular short fasts have been recommended by the yogis as an excellent health measure. Yogananda referred to an Armenian doctor, Grant Sarkisyan, who had treated many patients successfully with fasting therapy for such disorders as asthma, skin diseases, digestive problems, and early stages of arteriosclerosis and hypertension.

Fasting increases the process of elimination and the release of toxins from the colon, kidneys and bladder, lungs and sinuses, skin and purifies the blood. This process can generate discharge such as mucus from the gastrointestinal tract, respiratory tract, sinuses, or in the urine. This is helpful to clear out the problems that have arisen from overeating and a sedentary lifestyle. Much of aging and disease, results from biochemical suffocation, where our cells do not get enough oxygen and nutrients or cannot adequately eliminate their wastes. Fasting helps us decrease this suffocation by allowing the cells to eliminate and clear the old products. But we have also seen that clients who do not suffer from overeating nor a sedentary lifestyle, who have been vegetarians for years, have a build up of mucous layers in the gastro intestinal tract, and have experienced dramatic positive changes with our juice fasting program.

If you don't purge yourself of these toxins on a regular basis, toxemia gets worse and worse, until the body cannot stand it any longer and either purges itself spontaneously in form of diarrhea, acne, pimples, boils, 'liver spots', foul perspiration, body odor, bad breath, and so forth, or else it simply gives up the battle and succumbs to cancer, tuberculosis and other fatal conditions.

Fasting also eliminates acidosis from the bloodstream itself. In fact, the unpleasant side effects felt during the first three days of a fast are due entirely to these acid crystals and other toxins entering the bloodstream en masse for elimination.

Detoxification is the foremost argument presented by advocates of fasting. "Detoxification is a normal body process of eliminating or neutralizing toxins through the colon, liver, kidneys, lungs, lymph glands, and skin. This process is precipitated by fasting because when food is no longer entering the body, the body turns to fat reserves for energy. "Human fat is valued at 3,500 calories per pound," a number that would lead one to believe that surviving on one pound of fat every day would provide a body with enough energy to function normally. These fat reserves were created when excess glucose and carbohydrates were not used for energy or growth, not excreted, and therefore converted into fat. When the fat reserves are used for energy during a fast, it releases the chemicals from the fatty acids into the system which are then eliminated through the aforementioned organs. Chemicals not found in food but absorbed from one's environment, such as DDT, are also stored in fat reserves that may be released during a fast. One fasting advocate tested his own urine, feces and sweat during an extended fast and found traces of DDT in each.

A second prescribed benefit of fasting is the healing process that begins in the body during a fast. During a fast energy is diverted away from the digestive system due to its lack of use and towards the metabolism and immune system. The healing process during a fast is precipitated by the body's search for energy sources. Abnormal growths within the body, tumors and the like, do not have the full support of the body's supplies and therefore are more susceptible to autolysis. Furthermore, "production of protein for replacement of damaged cells (protein synthesis) occurs more efficiently because fewer 'mistakes' are made by the DNA/RNA genetic controls which govern this process." A higher efficiency in protein synthesis results in healthier cells, tissues and organs.This is one reason that animals stop eating when they are wounded, and why humans lose hunger during influenza. Hunger has been proven absent in illnesses such as gastritis, tonsillitis and colds. Therefore, when one is fasting, the person is consciously diverting energy from the digestive system to the immune system.

Finally, the most scientifically proven advantage to fasting is the feeling of rejuvenation and extended life expectancy. Part of this phenomenon is caused by a number of the benefits mentioned above. A slower metabolic rate, more efficient protein production, an improved immune system, and the increased production of hormones contributes to this long-term benefit of fasting. In addition to the Human Growth Hormone that is released more frequently during a fast, an anti-aging hormone is also produced more efficiently. The only reliable way to extend the life span of a mammal is under-nutrition without malnutrition. A study was performed on earthworms that demonstrated the extension of life due to fasting. The experiment was performed in the 1930s by isolating one worm and putting it on a cycle of fasting and feeding. The isolated worm outlasted its relatives by 19 generations, while still maintaining its youthful physiological traits. The worm was able to survive on its own tissue for months. Once the size of the worm began to decrease, the scientists would resume feeding it at which point it showed great vigor and energy. The life-span extension of these worms was the equivalent of keeping a man alive for 600 to 700 years.

It seems that there are many reasons to consider fasting as a benefit to one's health. The body rids itself of the toxins that have built up in our fat stores throughout the years. Fasting purifies the blood, the body heals itself, repairs all the damaged organs during a fast. And finally there is good evidence to show that regulated fasting contributes to longer life.

However, many doctors warn against fasting for extended periods of time without supervision.