Yom Kippur and the Science of Fasting

Last week, I along with millions of people took off work and went 25 hours without food or water. No, we weren’t orchestrating a spontaneous hunger strike; we were observing Yom Kippur, the holiest day of the Jewish calendar. The instruction to fast comes from the Bible, but the Bible also tells us to do all kinds of other things—sacrifice animals, stone adulterers—that even the most pious ignore today. So why do we continue to find this one relevant? I believe the answer can be sought not just in religious texts, of which I confess to being almost entirely ignorant, but also in science.

Maurycy Gottlieb’s “Jews Praying in the Synagogue on Yom Kippur”

Physiologically, fasting sets off a chain of chemical and electrical signals in the body. After the stomach empties the last bits of a meal into the small intestine, it releases a hormone called ghrelin, which activates a region deep in the brain known as the hypothalamus. The hypothalamus then sends out a nerve signal that manifests as hunger, and we feel an unpleasant sensation in our stomach. That meal we ate also provided a surge in glucose, a simple sugar that fuels the brain, and when the surge ends we feel weak, tired, and sluggish until our next meal.

I’m familiar with the bodily effects of hunger, but I also notice changes in my mental state when I fast. The hyperactive part of my brain that normally wants to execute plans and think a million things—what Buddhists sometimes call the “monkey mind”—seems to shut down, or at least quiet down. I feel grumpy and pessimistic; I become contemplative; I write; if I go to services, I feel more like praying than I normally would. I also notice a heightened sense of connection to others. In an intangible but distinct and sometimes powerful way, I feel linked to people in other places who are also fasting now, as well as to people who have fasted in other times.

I began wondering this year if there was a connection between fasting and what was happening in my brain. If I were a neuroscientist, I could put some fasting people in MRI machines, like what Richard Davidson at the University of Wisconsin does with meditating monks. But I’m a writer, not a scientist, so I did the unscientific thing and called a few friends.

For Rhea Kennedy, who has fasted on Yom Kippur for many years, going without food doesn’t necessarily lead to turning inward (“I’m usually pretty introverted anyway,” she observes), but she does find herself feeling profound empathy with “other people who can’t eat for some reason.” Rhea also feels herself linked with people who lived in the past. “It affects the way I relate to my Jewish ancestors and survivors of the Holocaust,” she says. “A lot of [their experiences] had to do with food deprivation.”

Laura Bellows, another friend with a long history of fasting, echoes Rhea’s experience of empathy with those for whom going without food may not be a choice. “It makes me feel like this is a little taste of what it’s like to be hungry,” she says. Laura also finds that fasting enhances the intensity of her prayers, and creates a sense of bonding with her community. “I feel very connected to those with whom I’ve fasted,” she says. “It’s as if we’ve been through this communal hardship together.”

Muslims also report feeling empathy during fasting for Ramadan. Here are a couple of examples:

“At one point he [a Washington, DC taxi driver] said that Ramadan and fasting have a broader social impact because they are ‘a reminder of people who cannot eat,’ and how lucky we are.” (from the blog No Kid Hungry)

“When [Emad Meerza, a Muslim community leader in Bakersfield, CA] fasts, he thinks about others around the world who are also fasting — not by choice, but because of famine, war or political strife. Through our own suffering, he says, empathy is born.

‘The only way to feel that is to feel a little bit of that pain,’ he says.”

(from the Bakersfield Californian)

These are anecdotes, not even close to the kind of data that would be needed to approach this question scientifically. Unfortunately, from what I can tell, scientists haven’t sought the answer either. I conducted article database searches on various combinations of terms like “Yom Kippur,” “fasting,” “psychology,” “science,” “empathy,” “mental states,” “hunger,” and “food deprivation,” but turned up little that seemed to address a link between religious fasting and the brain. Maybe I’m missing it—if you know of such a study, please drop me a line; I’d love to know about it.

Might Jews, Muslims, Mormons, Hindus, and others have developed and maintained fasting practices in part because they understood a mind-body connection that scientists have yet to make? Empathy is a near universal human experience, and has also been observed in rats and monkeys. But it has been a puzzle for neuroscience to figure out how one brain can share an experience occurring in another, entirely distinct brain.

Recently, some scientists have looked to systems of nerve cells known as mirror neurons, which are thought to fire in ways that mimic what we believe to be happening in the brains of others. V. S. Ramachandran, a neuroscientist at the University of California, San Diego and a prominent mirror neuron proponent, has even called them “empathy neurons.” Other scientists question this link, and some doubt whether humans truly have neurons dedicated to mimicking others’ brain activity. But whether due to mirror neurons or not, I do find it suggestive that our processing centers for emotions like empathy seem to be located not in the thought-processing and decision-executing regions of the brain—the frontal lobes—but in deeper regions of the brains. Our understanding of the neurological basis of empathy is described in a paper by psychologists Stephanie Preston of the University of California at Berkeley) and Frans de Waal of Emory University.

Which lobe contains empathy?

Does that mean thinking and deciding require more fuel than emoting? Many times I have become extremely hungry after doing sustained, mentally demanding work, suggesting to me that concentrating hard and long might demand more energy than, say, sitting by a stream. But while some studies have shown that people do better on certain difficult mental tasks when supplied with a sugary drink, it seems that in general the brain consumes a nearly constant amount of fuel no matter what it’s doing. Ferris Jabr wrote a good review of some of this research for Scientific American recently.

Regardless, hunger does seem to make it hard to concentrate on the kinds of tasks we normally think of as “work.” I’ve had that experience, Rhea and Laura both reported it, and so did Jonah Lehrer. It happens to millions of office workers every day; it’s why schools provide free breakfast to students. Perhaps it’s mainly because we get distracted by hunger, but for some reason we can’t seem to concentrate and think well without food in our stomachs. On the other hand, we can contemplate, pray, and feel connected.

My naïve hypothesis, then, is that fasting may quiet the noisy thought-processing and decision-making brain regions, and give us a chance to listen to a softer, less pushy voice—one that has less to say about the day-to-day that consumes us most of the time, but a lot to say about the longer and deeper currents that run under our lives. And one of those currents seems to be a sense of connection to other living beings on our planet. Fasting is not sufficient to hear this voice—we also need to choose to listen, perhaps by going to a prayer service, or by spending time in a quiet place. (Lehrer in his blog post described a fast not leading to a religious state of mind.) But maybe fasting makes the listening easier.

Many in the popular press continue to write about the supposed rift between science and religion. (See a Time article, a Discover blog post, and a 2010 book for some examples.) Ritual fasting seems to me like a perfect meeting place, where science can help elucidate the value of religious traditions, and religion can stimulate scientific investigation. I’d love to see scientists take on this kind of research.


One Comment on “Yom Kippur and the Science of Fasting”

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