Fasting is a practice that Jews and Muslims, believers and scientists, Deepak Chopra and Glenn Beck all embrace. But does going without food really deliver spiritual and physical benefits? Bruce Feiler investigates.

If you’re looking for a way to bring together believers and scientists, here’s a tip that could remind them of their commonality and save money, too: No food!

Fasting may be the one activity these days that unites the religious and the secular, the left and the right, Deepak Chopra and Glenn Beck.

Abnegation is a way of adding oomph to any ritual; putting your stomach where your mouth is. It’s like saying, “Hey, God, I really mean it!”

As Muslims look back on a month of daytime fasts, Jews observe a 24-hour fast to observe the Day of Atonement, and Glenn Beck initiates a daylong fast to honor the Founding Fathers, the time seems ripe to ask: Does fasting work? Can it, as the prophets suggest, expiate our sins and bring us closer to God? Can it, as the yogis propose, purge our toxins and improve our sex lives? Can it, as researchers hypothesize, cure our jet lag and help us get pregnant?

In short, can fasting save the world?

Fasting pops up in an astonishing array of cultures around the world, from the Babylonians to the Incas, the Confucians to the Jains, which suggests that abstaining from food is one of the core impulses of religion, right up there with mourning, marriage, and sexual regulation. Abnegation is a way of adding oomph to any ritual; putting your stomach where your mouth is. It’s like saying, “Hey, God, I really mean it!”

In the Abrahamic faiths, the notion of fasting appears in the Hebrew Bible, the New Testament, and the Koran, but generally speaking the practice seems to grow more important over time. The patriarchs don’t fast, but Moses does. The kings fast some (especially David, who Biblically had lots of sins to atone for), but the prophets even more. Christians fast more than Jews; Muslims more than either. One explanation might be that as religion became more organized, diverse, and international, fasting as a way of imposing universal authority on far-flung, disparate people became more central to the priestly class.

Fasting in the Bible is both personal and political. Individuals abstain from food to express contrition (Ahab) or to prepare for divine revelation (Moses). In a precursor to hunger strikes today, leaders also fast to prepare troops for battle (Samuel) or to request divine aid for a political cause (Ezra). Jesus fasted for 40 days but warned others not to starve themselves for public show. (What would he have said about a 2003 publicity stunt in which David Blaine starved himself for 44 days in a glass box over the Thames and lost 25 percent of his body weight?)

Eastern religions stress a different reason for fasting, namely that it cleanses the body and purifies the mind. The Indian tradition of Ayurveda, espoused by both Buddhists and Hindus and endorsed by Deepak Chopra, holds that the body is 80 percent liquid and that fasting purges corrosive toxins and restores proper balance. The Jains have a ritual of voluntary death by fasting, which they distinguish from suicide because of the prolonged period of contemplation and preparation.

So is any of this backed up by science?

The normal instinct of scientists is to scoff at religious rituals as primitive and naïve, coming from that pitiable time before the invention of the lab coat. And scientists do, indeed, downplay many of the supposed benefits of abstaining from food. For starters, your vital organs already do a pretty good job of dispensing with toxins. Second, fasting is not a good strategy for losing weight—after about half a day of not eating, the body turns to muscle and fat for fuel, then eventually slows down its metabolism, so that once you start eating again, any weight loss is quickly reversed.

But a host of new studies suggest that tactical fasting can be beneficial in a surprising number of circumstances:

Arthritis. A Norwegian study by Jens Kjeldsen-Kragh and others (2000) concluded that a seven- to 10-day controlled fast is effective in improving rheumatoid arthritis, but only if followed by a strict vegetarian diet. Patients who returned to eating normally lost all benefits.

Fertility. A study by Jonathan Tilly of Harvard Medical School, released this month, shows that reducing the caloric intake of older mice by 40 percent significantly reduces the number of eggs with abnormal chromosomes. A similar study by Tilly last year concluded that restricting food intake of adult mice extended their reproductive lifespan and the health of their offspring.

Jet lag. Harvard’s Clifford Saper published a study last year demonstrating that when mice eat no food for about 16 hours, their body clocks adjust much more rapidly to jet lag. Though untested on humans, the study suggests that the desire to eat is greater than the desire to sleep, so the body opts to postpone rest for fuel, thereby resetting its circadian cycle.

Aging. Everyone agrees that reduced caloric intake boasts a host of medical benefits, but research by Marc Hellerstein, at Berkeley, suggests that targeted fasting, such as every other day, coupled with a healthy diet, can shows signs of slowing cancer and reducing aging.

Given this continued fascination with fasting in both the laboratory and the pew, the urge not to eat would appear to be as universal as the desire to eat. Even more tantalizing, both sides can claim to be right. Fasting is that rare endeavor that believers and scientists can agree is beneficial. With that mutuality, the old parable may need a new spin. The fastest way to a man’s heart just may be through an empty stomach.

by Bruce Feiler