For thousands of years people have fasted to cleanse the body and the spirit. And, of course, many fast to lose (some) weight. Recently, a growing body of scientific research seems to suggest that fasting may slow the aging process.
[div class=attrib]From the New Scientist:[end-div]
THERE’S a fuzz in my brain and an ache in my gut. My legs are leaden and my eyesight is blurry. But I have only myself to blame. Besides, I have been assured that these symptoms will pass. Between 10 days and three weeks from now, my body will adjust to the new regime, which entails fasting for two days each week. In the meantime, I just need to keep my eyes on the prize. Forget breakfast and second breakfast, ignore the call of multiple afternoon snacks, because the pay offs of doing without could be enormous.
Fasting is most commonly associated with religious observation. It is the fourth of the Five Pillars of Islam. Buddhists consider it a means to practise self-control and advocate abstaining from food after the noon meal. For some Christians, temporary fasts are seen as a way of getting closer to God. But the benefits I am hoping for are more corporeal.
The idea that fasting might be good for your health has a long, if questionable, history. Back in 1908, “Dr” Linda Hazzard, an American with some training as a nurse, published a book called Fasting for the Cure of Disease, which claimed that minimal food was the route to recovery from a variety of illnesses including cancer. Hazzard was jailed after one of her patients died of starvation. But what if she was, at least partly, right?
A new surge of interest in fasting suggests that it might indeed help people with cancer. It could also reduce the risk of developing cancer, guard against diabetes and heart disease, help control asthma and even stave off Parkinson’s disease and dementia. Many of the scientists who study fasting practise what they research, and they tell me that at my age (39) it could be vital that I start now. “We know from animal models,” says Mark Mattson at the US National Institute on Aging, “that if we start an intermittent fasting diet at what would be the equivalent of middle age in people, we can delay the onset of Alzheimer’s and Parkinson’s.” Surely it’s worth a try?
Until recently, most studies linking diet with health and longevity focused on calorie restriction. They have had some impressive results, with the lifespan of various lab animals lengthened by up to 50 per cent after their daily calorie intake was cut in half. But these effects do not seem to extend to primates. A 23-year-long study of macaques found that although calorie restriction delayed the onset of age-related diseases, it had no impact on lifespan. So other factors such as genetics may be more important for human longevity too (Nature, vol 489, p 318).
That’s bad news for anyone who has gone hungry for decades in the hope of living longer, but the finding has not deterred fasting researchers. They point out that although fasting obviously involves cutting calories – at least on the fast days – it brings about biochemical and physiological changes that daily dieting does not. Besides, calorie restriction may leave people susceptible to infections and biological stress, whereas fasting, done properly, should not. Some even argue that we are evolutionarily adapted to going without food intermittently. “The evidence is pretty strong that our ancestors did not eat three meals a day plus snacks,” says Mattson. “Our genes are geared to being able to cope with periods of no food.”
What’s in a fast?
As I sit here, hungry, it certainly doesn’t feel like that. But researchers do agree that fasting will leave you feeling crummy in the short term because it takes time for your body to break psychological and biological habits. Less reassuring is their lack of agreement on what fasting entails. I have opted for the “5:2” diet, which allows me 600 calories in a single meal on each of two weekly “fast” days. The normal recommended intake is about 2000 calories for a woman and 2500 for a man, and I am allowed to eat whatever I want on the five non-fast days, underlining the fact that fasting is not necessarily about losing weight. A more draconian regimen has similar restricted-calorie “fasts” every other day. Then there’s total fasting, in which participants go without food for anything from one to five days – longer than about a week is considered potentially dangerous. Fasting might be a one-off, or repeated weekly or monthly.
Different regimens have different effects on the body. A fast is considered to start about 10 to 12 hours after a meal, when you have used up all the available glucose in your blood and start converting glycogen stored in liver and muscle cells into glucose to use for energy. If the fast continues, there is a gradual move towards breaking down stored body fat, and the liver produces “ketone bodies” – short molecules that are by-products of the breakdown of fatty acids. These can be used by the brain as fuel. This process is in full swing three to four days into a fast. Various hormones are also affected. For example, production of insulin-like growth factor 1 (IGF-1), drops early and reaches very low levels by day three or four. It is similar in structure to insulin, which also becomes scarcer with fasting, and high levels of both have been linked to cancer.
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