Health Benefits of Fasting and Caloric Restriction?

She says it was a sad day Prohibition ended because Dad gets the drink going around to saloons offering to sweep out the bars and lift barrels for a whiskey or a beer. Sometimes he brings home bits of the free lunch, rye bread, corned beef, pickles. He puts the food on the table and drinks tea himself. He says food is a shock to the system and he doesn’t know where we get our appetites. Mam says, They get their appetites because they’re starving half the time.

plateIs food a shock to the system? The above quote is from Angela’s Ashes, and describes the author Frank McCourt’s father, a man as thin as a rail, who often swore off food. Although he was certainly no paragon of health, as evidenced by his smoking and heavy drinking, there may be a kernel of truth in his assessment of food as “a shock to the system.”

I thought of this quote while talking with a Muslim friend. He’s fasting from sunrise to sundown as part of the observance of Ramadan, and tells me that he only eats at night before bed. In reflecting upon my own experience I realize that I have rarely fasted, and I have never gone without food for an entire 24 hour period in my whole life. How weak and addicted. I hereby resolve that I will pick a day soon and eat nothing (except for drinking water), just for the exercise in self-control it represents.

But does the sustained restriction of calories or intermittent fasting have health benefits (in addition to perhaps boosting one’s sense of pride)? From Wikipedia:

Research suggests there are major health benefits to caloric restriction. Benefits include a reduced risk of cancer, cardiovascular diseases, diabetes, insulin resistance, immune disorders, and more generally, the slowing of the aging process and the potential to increase maximum life span. According to Dr. Mark P. Mattson, chief of the laboratory of neurosciences at the National Institute on Aging, fasting every other day (intermittent fasting) shows as strong of beneficial effects as caloric-restriction diets in mice, though no studies have been done in humans to date.

According to The National Academy of Sciences other health benefits include stress resistance, increased insulin sensitivity, reduced morbidity, and increased life span. Long term studies in humans have not been conducted. However, short term human trials showed benefits in weight loss.

There was a study published in Science earlier this summer looking at Rhesus monkeys fed 30% less than a usual control group of monkeys. Those eating a restricted calorie diet developed less cancer, diabetes, heart and brain disease. The restricted monkeys seemed to die less of chronic disease and old age, although overall their longevity was not statistically different from the control group.

Fasting and caloric restriction are not new concepts of course. Most religions employ some elements of both in their rituals. Christianity, Hinduism, Islam, Judaism, Jainism, Sikhism, and Buddhism all contain some degree of fasting in their doctrine and practice. In a religious context this is motivated by a sense of spiritual cleansing and control over base instincts, but its near universality would seem to hint at an underlying, intuitive survival benefit.

One theory which might explain the observed decrease in cancer from caloric restriction and fasting is that the constant process of replication is interrupted, and that the body pauses for a moment when fuel is scarce, allowing time to mend damages:

Cancer is essentially the uncontrolled division of cells, and its development typically requires the presence of multiple mutations. “Normally, a cell will try to fix any damage that has occurred to its DNA,” said Hellerstein, “But, if it divides before it has a chance to fix the damage, then that damage becomes memorialized as a mutation in the offspring cells. Slowing down the rate of cell proliferation essentially buys time for the cells to repair genetic damage.”

A sobering point of view comes from another study which directly challenges the notion that caloric restriction is universally good, and instead finds benefit or harm directly related to the weight of the mice under study:

If you are a mouse on the chubby side, then eating less may help you live longer. For lean mice – and possibly for lean humans, the authors of a new study predict – the anti-aging strategy known as caloric restriction may be a pointless, frustrating and even dangerous exercise….

“Your energy expenditure and your energy intake should be in balance,” Sohal said. “It’s as simple as that. And how do you know that? By gain or loss of weight. “The whole thing is very commonsensical.”

For humans of normal weight, Sohal strongly cautions against caloric restriction. In a 2003 study, he and Forster found that caloric restriction begun in older mice – both in DBA and leaner C57 individuals – actually shortened life span.

It is unclear whether caloric restriction and fasting are beneficial to humans. Many studies of short-lived animals show benefit, but there are also studies showing that a trend towards longevity and better health is not universal and may depend upon individual factors such as total weight and genetic make up. The only unequivocal proponents of caloric restriction seem to be the purveyors of dieting books and resveratrol, a compound which mimics the biochemical effects of calorie restriction. Almost predictably, resveratrol shows impressive results for fruit flies and yeast, but not really humans to this point.

I’m going to do that fasting day anyway, the one where I drink only water to test my self-discipline, self-mastery, and self-respect as a rather unchallenged, middle class American who has never faced the horrors of hunger and famine. I would agree with Frank McCourt’s father that food often does feel like “a shock to the system,” a feeling I can most vividly associate with eating a 7th helping of chicken fingers at my college cafeteria one night, and then going home to lie curled up in bed, writhing in digestive agony.

But the guiding principle, in my opinion, is that great food is one of life’s supreme pleasures, and who really wants to chance missing that?


5 thoughts on “Health Benefits of Fasting and Caloric Restriction?

  1. #1 Dinosaur

    May I suggest designating Monday, September 28th as your fast day. Start it after dinner the Sunday before, and don’t eat anything until after sunset that Monday.

    For what it’s worth, I shall be fasting that day as well, as I do for a day every year, as will many of my co-religionists. Even if not as a practicing Jew, consider it an exercise in solidarity with civilization’s first monotheists.

  2. robin andrea

    It seems the only time people are subjected to the need to fast these days is in preparation for the dreaded colonoscopy. What a terrible association. But I have read of people who choose for themselves to fast one day a week, or one day month as a cleansing and healthful ritual. Some part of me thinks it just sounds right to give the body a break. Our obsession with food and its non-stop availability have already had such negative effects in so many ways. It’s been many years since I fasted for Yom Kippur. I like the idea now, perhaps not so much for atonement, but for the more corporeal benefits. Perhaps atonement will follow.

  3. yaser

    You might want to have an early morning breakfast before dawn (which is what Muslims do) — which might make it easier =)

  4. hat_eater

    I had to fast for three days pending my gastroscopy and I noticed that while the acute syndroms were concentrated in the first 24 hours, the real cravings came on the third day. Then I was allowed to eat some unsalted rice pudding – oh, what a treat it was!
    Later, when I could eat an apple, it was better than anything I ever tried.
    I recommend fasting once for 72 hours to appreciate the food more. Only if circumstances allow, of course – on the third day I was so weak I had to really concentrate to walk straight without grabbing the walls.

  5. kt

    there is alot of interesting research on fasting. including decreasing high blood pressure, cholesterol, weight etc. Not to mention cleansing the mind. Up to 72hrs can do the body good and then I notice I tend to crave “natural” foods that are made from earth. I say this as I am drinking a glass of wine with nutella as a side snack. hmmm maybe i should do a fast as well.

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