Fasting is the age-old practice of limiting food and drink, often as part of religious festivals. Some fasts restrict all food, while others allow a stripped-down diet. Fasts may also go hand-in-hand with non-food restrictions, such as religious rules forbidding fighting, lying, and sex. (Fasts are notorious for lumping sin and pleasure together into one giant category of forbidden pastimes.)
The benefits of fasting aren’t digestive. Supporters point out how practicing selfrestraint (and enduring a little borborygmus) develops inner will. They’re less likely to point out the way fasting increases carnal pleasures post-fast. Much in the same way that you feel good when you stop striking your head against a tree, the end of a fast brings a heightened appreciation of everything you temporarily sacrificed. More controversially, fasts are sometimes studied as a way to improve health. Some studies suggest that occasional fasting or lifelong calorie restriction can boost life expectancy.
One possible reason for this phenomenon (if it actually exists) is that gentle stress may prompt the body to fire up certain beneficial repair processes. Or it may simply be that less food means less of all the ills of the modern diet—from excess sugar to runaway fat.
The score for so-called detoxifying diets is far less promising. Promoters suggest that extreme fasting, bizarre diet restrictions, or colon “cleansing” can purge toxins from your body. The idea is alluring— after all, who wouldn’t like to atone for a lifetime of dietary sin and return the body to a pristine, unpolluted state? However, the science is about as solid as a bowl of low-calorie Jell-O.
Source of Information : Oreilly - Your Body Missing Manual