Skip To Content
Back to Opinion

Why Fasting Is Good for Body and Soul

What does “fasting” mean? As a physician, I tell patients not to eat after midnight so that the morning’s laboratory tests can be compared against known standards (it would be hard to determine whether someone truly has high cholesterol if the level was measured after they ate a Big Mac). From a religious standpoint, fasting can mean eating nothing during the day (as in the Bahá’í month of Ala, or during Ramadan in Islam), eating only once a day (as in Coptic Orthodox Churches), not eating for a full day (as in Judaism, or on Good Friday and Ash Wednesday in Catholicism) or just avoiding certain foods (such as meat). From a health standpoint, there has been a recent upsurge in interest in intermittent fasting for good health (as in Alternate Day Fasting, the Warrior Diet, Leangains or the Periodic Fast.)

I have spent more than 25 years studying the biology that makes it so hard to keep weight off. I have also had the opportunity to lead a number of discussions at the Stephen Wise Free Synagogue in New York, regarding the intersections of religion and science. I thought I would consider whether the physiology of fasting helps us achieve spiritual goals.

The reasons for fasting are as varied as the methods. I respect them all, but can discuss only mine. Yom Kippur is the most observed fast day among Jews. As a child I believed that at least trying to fast on Yom Kippur was a way of atoning for my my multitudinous real and perceived sins during the year. As a medical student, I thought of fasting as self-empowerment in which the mind overcomes the body’s desires and also toys with mortality (watch Discovery Channel’s “Naked and Afraid” to be reminded of how much we need food and water). Now I hope to move away from my usual concerns and be introspective regarding our physical and spiritual places in the world.

Barring midnight snacks, we routinely fast for about eight to 12 hours each night. Once the nutrients from our last meal have been absorbed, we first break down our liver glycogen stores into glucose for fuel. Over time, we depend less on glucose and more on the oxidation of fat for our energy. Hence, much of the hype for the intermittent fast to lose weight.

The physical effects of fasting (such as a rumbling stomach) are much more predictable than the psychological effects. Short-term fasting increases our self-awareness — our sensation of our life essences, our heart rate and, of course, our hunger while decreasing our accuracy in processing and reacting to information from the outside world.

Fasting results in rather complicated changes to our bodies’ chemistry. We make less insulin and more of various other molecules, including growth hormone, glucocorticoids, glucagon, adrenalin, noradrenalin and dopamine. For more than 50 years it has been known that mild increases in these hormones enhance memory and concentration. Adrenalin, noradrenalin and dopamine in particular are stress hormones, all called “catecholamines,” and are similar to psychostimulant medications used in attention deficit disorder. They act coordinately to increase attentiveness, memory (especially for emotional events) and our ability to construct a hierarchy of what is important.

Over time we can’t keep our blood sugars in their usual range. For some of us, that hypoglycemia will also slow down our thinking processes and make us a little sluggish and disoriented, sometimes to the point that we feel we have had an out of body experience. We each have to decide whether this experience was biological, spiritual or both.

To be sure, each person has his or her own reasons for fasting. I agree with them all. Fasting is an extremely personal experience, but it does seem that its physiology may aid us in having a spiritual experience beyond suffering our hunger and demonstrating our willpower and faith.

It is quite amazing how often rituals, whether divinely or anthropologically dictated, are actually good for us. Religious participation and optimism have been associated with better physical and mental health and [longevity][23]. Dicta to avoid certain foods also encourage breeding of animals most likely to thrive in the pre-industrialized environment as well as aiding in protection against certain diseases and promoting a more balanced dietary intake. Physiology and religious observance also complement each other in safeguarding the reproductive integrity and survival of our species. Sexual practices, such as engaging in intercourse only during the midcycle, when a woman is most likely to be fertile, maximize the chances of conceiving. Perhaps we can add fasting to this list of “body and soul.”

Michael Rosenbaum is a professor of pediatrics and medicine at Columbia University Medical Center and an Op-Ed Project Public Voices fellow.

[23]: Involvement and US Adult Mortality.pdf


Republish This Story

Please read before republishing

We’re happy to make this story available to republish for free, unless it originated with JTA, Haaretz or another publication (as indicated on the article) and as long as you follow our guidelines. You must credit the Forward, retain our pixel and preserve our canonical link in Google search.  See our full guidelines for more information, and this guide for detail about canonical URLs.

To republish, copy the HTML by clicking on the yellow button to the right; it includes our tracking pixel, all paragraph styles and hyperlinks, the author byline and credit to the Forward. It does not include images; to avoid copyright violations, you must add them manually, following our guidelines. Please email us at [email protected], subject line “republish,” with any questions or to let us know what stories you’re picking up.

We don't support Internet Explorer

Please use Chrome, Safari, Firefox, or Edge to view this site.