Research done in both lab animals and humans has shown that there may be a connection between restricted caloric intake and longevity. In other words, fasting may make you live longer. These studies have shown that restricting calories improved some of the markers of aging, such as body temperature and insulin levels. These kinds of improvements could delay the onset of age-related illnesses such as Alzheimer's disease, diabetes and heart disease.

Potential Dangers of Fasting
Fasting for extended periods of time can cause malnutrition, depletion, weakness and a weakened immune system. The body needs a variety of nutrients in order to function, and extended fasting robs the body of proper nutrition, especially proteins. Protein deficiency is the leading cause of starvation deaths seen in Third World countries. For these reasons fasting is not recommended for longer than seven to 10 days.

Who Should Not Fast
People with diabetes should avoid fasting -- it may cause spikes and drops in blood sugar and insulin levels. Because of the potential for protein deficiency, pregnant or lactating women should also avoid fasting. People who suffer from the following conditions or are in any of the following situations should also steer clear of fasting diets: underweight, fatigue, low immunity, weak heart, low blood pressure, cardiac arrhythmias, pre- and post surgery, mental illness, cancer, peptic ulcers and nutritional deficiencies.

How to Fast Properly
First-time fasters should start off slowly, fasting one or two meals or during a 12- to 14-hour period in the evening, during sleep. First-timers should also consult a doctor before fasting to ensure that they are not putting their bodies at risk.