Yesterday was Yom Kippur, the Jewish holiday of atonement. It's traditional to fast on Yom Kippur for all the usual religious reasons - not eating is a way to elevate the spirit and purify the mind (or so says the Talmud). It makes the sacred day feel a little less ordinary.

I have to confess: I'm a terrible faster. When I don't eat, my thoughts don't become more ethereal and holy - they become fixated on calories, so that the only thing I can listen to is the impatient gurgling of my stomach. (My belly drowns out the sermon.) I get cranky and tired and squander hours daydreaming about ice cream - my wife tells me that I regress into a five year old. (After a single day of fasting, I'm in awe of Muslims who fast for the entire month of Ramadan. I have no idea how they do it.)

This year, I pledged to act more mature. I promised myself I wouldn't complain about not being able to eat. So how would I distract myself from thoughts of the fridge? I decided to work on an article during the afternoon and pledged to spend a few hours playing with sentences (not very holy, I know.) It didn't take long, however, before I realized that I was wasting my time - I was utterly unable to focus or think in clear thoughts; my prose was even more more garbled than usual. I then decided to read a few papers for work. Once again, my mind rejected the premise: after a few paragraphs of dense prose, I was fast asleep, kidnapped by a nap.

For me, the lesson was rather obvious: my brain needs glucose like my laptop needs alternating current. Even a few hours without food means that I'm running on reserve power; I could feel my executive function (and my frontal lobes) begin to sputter and quit. And then I passed out.

This reminded me of a clever study I describe in How We Decide:

Look, for example, at this experiment led by psychology graduate student E.J. Masicampo and Roy Baumeister, an eminent psychologist at Florida State University. The experiment began with a large group of undergraduates performing a mentally taxing activity that involved watching a video while ignoring the text of random words scrolling on the bottom of the screen. (It takes conscious effort to not pay attention to salient stimuli.) The students were then offered some lemonade. Half of them got lemonade made with real sugar, and the other half got lemonade made with a sugar substitute. After giving the glucose time to enter the bloodstream and perfuse the brain (about fifteen minutes), Baumeister had the students make decisions about apartments. It turned out that the students who were given the drink without real sugar were significantly more likely to rely on instinct and intuition when choosing a place to live, even if that led them to choose the wrong places. [The experiments assessed this by looking at their vulnerability to the "attraction effect," which occurs when a difficult choice is swayed by the presence of an irrelevant decoy option.] The reason, according to Baumeister, is that the parts of the brain responsible for careful, rational deliberation were simply too exhausted to think. They'd needed a restorative sugar fix, and all they'd gotten was Splenda. This research can also help explain why we get cranky when we're hungry and tired: the brain is less able to suppress the negative emotions sparked by small annoyances.

I'd love to see a comparative survey of how decisions change in Muslim countries during Ramadan. Given the Baumeister experiment, you'd expect to see a slight but consistent rise in the sorts of choices that tend to be associated with impulse, instinct and the reliance on lazy heuristics. Are people running more red lights? Making more impulse purchases on their credit card? Engaging in more stereotyping? The irony of fasting is that, although we think we're engaging in act of strict self-control, we're actually making it harder to resist other temptations. For a thorough survey of the relationship between self-control and glucose, check out this extensive review article, "Self-Control Relies on Glucose As A Limited Energy Source: Willpower is More Than A Metaphor".

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Ritual fasting is to actual fasting as ritual bathing is to actual hot soap-and-water bathing.

Actual fasting is going hungry.

Ritual fasting is making a show of going hungry while sneaking food on the sly. Insiders know this. It makes the trusting fools who actually go hungry admire the determination of the cheaters.

I wonder if this isn't the point of fasting: to favor emotional centers over more rational ones.

This reminds me of my upbringing in the Mormon (Latter-Day Saint or LDS) Church.

Fasting is crucial to the LDS faith. The first Sunday of each month involves a 2-meal, 24-hour fast â no food or drink, not even water. Instead of Sacrament Meeting (the usual worship service) the faithful take part in Fast and Testimony Meeting. Members who desire take turns, rising from their seats in the congregation and bearing their testimony.

This consists of an extemporaneous testimonial or confessional (other faiths call it witnessing or confessing). These testimonies are often tear-filled and emotional â the more emotional, the better. They usually involve language of personal conviction and certainty: 'I know The Church is true. I know that Joseph Smith was a Prophet of God. I know that Jesus is the Christ.'

Fasting puts both the speaker and the hearer in a different (and less rational) frame of mind: more prone to tearful self-revelation and more receptive to conditioning by peer approval and example.

I may not believe in the LDS Church any more, but I do believe that LDS Fast and Testimony Meeting is a powerful tool to foster fervent belief, uniformity of opinion, and in-group bonding. It reaches deep into the psyche of its participants.

By A. Man Zed (not verified) on 29 Sep 2009 #permalink

Ha ha ha ha... Your comments are messed up, but if you hit the post button with a blank comment, you can post from the "preview" section!

Anyway, Muslims only fast during the daylight. They eat a very big dinner and a huge, early breakfast. They're also able to get dispensations (including atonement deeds/actions) to drink during the day if it's required because of the necessity to work, medical condition, etc.

And there are other rules about being able to "legitimately" not fast during the day.

they needed to do an experiment to prove this? surely everyone knows you should never shop on an empty stomach. And that people quitting smoking can't resist food..

If you want an easier time of it, go on a ketogenic diet before the fast. Once your body is burning fat for fuel, then go on the fast. Early hunters needed stable blood sugar (which happens once you are finally burning ketones) in order to concentrate on the hunt.

I believe fasts are meant to recapture a mental state that an agriculturally based people would seldom enter into because of level of carbohydrate in their diets. Carbohydrate eaters are essentially conservative- stay, defend, and eat the food source until it's all gone. A hunter must search...

I've been fasting regularly (1-2x weekly) for the past year and have also conducted longer fasts (from 3-5 days) a few times in the past year. I am a practicing Mormon, so I have fasted once a month for the past 30 years. I guess you could say I'm used to fasting.

On one day fasts I typically find no diminished mental performance. I generally fast from lunch to lunch, and find that I am more alert the next morning. There are brief periods (usually just one in a one day fast), maybe lasting 5 or 15 minutes, where I have hunger pain, but these don't last long, and I return to normal after they pass.

Some argue that fasting leads to increased eating. That has not been true in my case. I used fasting to drop from 240 pounds to 190 pounds. It wasn't the only strategy I used (better eating and exercise too), but it is an important strategy I use to maintain my health.

On longer fasts, the mental alertness comes and goes. My last 5 day fast, the 2nd and 4th day were the toughest. Those days I had difficulty concentrating.

Personally, I find fasting enjoyable. Shorter fasts help me reduce calories and I believe my mental performance increases slightly. Longer fasts I use primarily as a means to cleanse myself, but I wouldn't do a long fast if I have to work. I also think that fasting has improved my discipline in eating healthy.

There are a lot of proponents of intermittent fasting such as Brad Pilon ( and Mark Sisson (

By Darin Woolwine (not verified) on 01 Oct 2009 #permalink

You might find the following information interesting:

The Eastern and Oriental Orthodox fast almost every Wednesday & Friday of the year. They also have two extended fasts, Lent and Advent (each about 40 days), in addition to two fasts lasting a couple weeks and several other single day fasts. Some of these fasts consist of complete abstinence from food. Others are mainly from dairy, meat and oil, and in much reduced quantity. Fasting in Orthodoxy also includes refraining from sexual intercourse.

For the Eastern Orthodox, fasting of various degrees of strictness takes up 180+ days of the year. The number is even higher for the Oriental Orthodox, at 250. Of course, as with any religious fast, the official rules will be strictly followed only by the devout.

When I was a student, I've read a book by this guy:
It was translated into Russian and very popular among my friends. I fasted for 36 hours every week during my last year at the University. I can swear fasting really helped me to concentrate and do all the work and pass the exit exams 1 year ahead of my group (packing 2 years of intensive study into 1 year, which I really needed to do).
I now live in US and can no longer fast, I blame the suggestive power of advertisement in US, as opposed to empty shelves and no ads in 1990s in Russia, which made it very easy not to think about food.

Personally, I find fasting enjoyable. Shorter fasts help me reduce calories and I believe my mental performance increases slightly. Longer fasts I use primarily as a means to cleanse myself, but I wouldn't do a long fast if I have to work. I also think that fasting has improved my discipline in eating healthy

my husband is baha'i and does the 19 day fast. I remember each year to go easy on him - he gets irritated more easily and makes impulse decisions.

So, yes, fasting for 19 days makes a difference in how ppl behave.