Now two things devour my life," wrote the poet William Butler Yeats. "The things that most of all I hate:/Fasting and prayers." This week, the world's billion Muslims and 12 million Jews will be fasting and praying in honor of Ramadan and Yom Kippur. Fasting is common to nearly every major religion; mystics fast to induce divine visions, and the rest of us fast to remind ourselves periodically that worldly pleasure is fleeting. Fasting is, in one respect, an exercise in discipline. "It's analogous to taking a vow of celibacy," says the atheist Sam Harris, who is interested in meditation. "It's not so much the direct effect of not having sex that is being sought, necessarily, but the freedom from all the related entanglements, hopes, cravings, etc."
Yes, but fasting, unlike celibacy, has immediate physical effects—stomach pangs, lightheadedness, fatigue—and one wonders whether the ancients, in their wisdom, understood the physiological interplay between starvation and feelings of transcendence better than we do. Scientists have not deeply studied the ways in which fasting alters the human brain, but Andrew Newburg, a radiologist at the University of Pennsylvania, has some ideas. Newburg looks at the effects of meditation on the brains of monks. He imagines that a brain deprived of fat and sugar may become "looser" or "more fluid," as he puts it: fasting may "open you up to these kinds of transcendent experiences." If you ask the starving brain to focus on a physical ritual—repetitive prayer, or a series of standing and kneeling positions, it may direct its shrinking stores of energy to those activities, further "loosening" its perceptions.
Scientists do believe that calorie restriction or intermittent fasting can lead to longevity and better health—at least in lab animals. Which brings to mind the legend of Saint Anthony, the third-century Egyptian who went alone into the desert after the death of his parents, shut himself into a cave, and lived on nothing but bread and water for two decades. When his friends finally broke down the wall of his cave, what they saw astonished them: "He was neither fat, like a man without exercise, nor lean," writes his biographer Athanasius. "His soul was free from blemish, for it was neither contracted as if by grief nor relaxed by pleasure." Through fasting and prayer, Anthony had become an angel.