Forget about cutting the carbs, bin the brown rice, dump the detox and stop chomping on raw carrots. If you want to lose weight, avoid heart disease, deafness and dementia, be happier and smarter and live longer, you might try a new approach – fasting.
These benefits may not be what the Archbishop of York, John Sentamu, had in mind when he went seven days without food in a tent inside York Minster recently to highlight the plight of those caught in the conflict between Lebanon and Israel. But his fast may have done wonders for his health; fasting is now being promoted in various guises as a way to a better, longer and lighter life.
That fasting works for weight loss isn't in doubt. In his 44 days in a suspended glass box, the magician David Blaine lost 24,5kg, about 25 per cent of his original body-weight. Fasting to such an extreme is unlikely to appeal to many, but research is showing that partial fasting – intermittent fasting or long-term calorie restriction diets – can have significant effects on weight and on many aspects of health, from asthma to heart disease.
It's claimed that the benefits go far beyond those achieved by simple weight loss, and that hunger and food deprivation somehow triggers a mechanism that puts the body into a survival mode. In these restrictive diets, daily consumption is cut by between 20 and 50 percent of normal, or no food is eaten on certain days. Partial fasting, with little eaten every other day, which has also been investigated, is designed to trigger the same kind of survival reactions as full fasting.
Evidence has built up since the 1930s that rodents, fish, fruit flies, worms, yeast and monkeys all benefit from fasting. The big question is whether the same benefits accrue to people. Three clinical trials involving the United States National Institute on Aging are under way, each investigating the idea that a reduced-calorie, nutritionally sound diet increases lifespan and prevents age-related chronic diseases such as cancer, diabetes and cardiovascular disease.
The early signs are that there are beneficial effects, and several other studies have found evidence that restriction or partial fasting can have significant health benefits. Work at Johns Hopkins University has shown that intermittent fasting and calorie restriction can slow the ageing of the brain and reduce the risk of diseases such Alzheimer's and Parkinson's.
Scientists at the universities of Wisconsin and Tokyo have found in animal studies that restriction can prevent age-related hearing loss by stopping or slowing the degeneration of hair cells in the cochlea.
When researchers at the University of Washington investigated men and women who had been on a diet for six years where their daily calorie consumption was half of normal levels, they found considerable benefits.
When they compared their hearts with people not on the diet, they found the hearts of dieters were more elastic, there was less furring up of the arteries, and the level of compounds involved in inflammation changed. "This is the first study to demonstrate that long-term calorie restriction with optimal nutrition has cardiac-specific effects that ameliorate age-associated declines," said Dr Luigi Fontana.
Similar effects have been found for other conditions, although the very long-term effects in humans, including any impact on longevity, are still largely unknown.
If there is an effect beyond that caused by weight loss itself, the puzzle remains as to what the mechanism could be. One suggestion is that fasting – full, partial or intermittent – and restriction affect metabolic rate, reducing free radicals and oxidative stress. Altered insulin sensitivity, greater stress resistance and changes in brain signalling are among other ideas.
A theory that hunger and a lack of food trigger a primitive survival response that provides better protection for the body's organs in times of famine is now in vogue. "Recent studies seem to favour a stress response that evolved early in most species to increase the chance of surviving adversity, such as calorie restriction," says Dr Eric Ravussin of the Pennington Biomedical Research Centre in Baton Rouge.
Benefits are said to start kicking in after two weeks, but just how it works is not clear. The researchers cite animal studies showing similar results, and it's suggested that one possibility is that the hunger and food deprivation turn on body mechanisms that lead to changes in the way the body processes fat.
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