Feel better: fast

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 last week in a tent inside York Minster 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 (54lb), 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 trigger a mechanism that puts the body into a survival mode.

In these restrictive diets, daily consumption is cut by between 20 and 50 per cent 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. "It is well established that, by reducing the number of calories required for weight maintenance to 60 to 70 per cent of normal, lifespan is increased up to 40 per cent, with near-perfect health across a broad range of species,'' says Dr James Johnson of Louisiana State University.

The big question is whether the same benefits accrue to people. Three clinical trials involving the US 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. Some beneficial effects seen in the fasting diets may also stem from the fact that they tend to be more nutritionally balanced that most diets.

The downside, of course, is that such restrictive diets may not be attractive to most people. Some research shows that most people prefer the novelty of trying different diets, even if they fail, and suggest that long-term diets that severely restrict intake are likely to fail in all but the most committed.

While David Blaine's style of fasting may be highly effective, Beyoncé Knowles's maple syrup may be more appealing, at least for 14 days - or until the next fad comes along.

The maple syrup plan

Thanks to Beyoncé Knowles, the "lemonade diet" is the fad of the moment. She says she lived on water, lemon, cayenne pepper and maple syrup for 14 days in order to lose 22 pounds for her role in the film Dreamgirls. The diet was first used more than 60 years ago by Stanley Burroughs, a naturopath, to treat ulcers. His book The Master Cleanser, detailing the diet, was published in 1976.

Burroughs believed that toxins in the blood were the root cause of ill health, and thatfresh lemon juice, purified water, maple syrup and cayenne pepper could help: the lemon juice cleans the body; cayenne boosts blood flow; and the syrup provides energy. Sceptics say that the benefits are down to weight loss and that people feel good because they're slimming down and sleeping better.

The diet (from themastercleanser.com)

For a minimum of 10 days, drink:

2 tablespoons (1 fluid ounce) fresh-squeezed lemon or lime juice;

2 tablespoons (1 fluid ounce) organic grade-B maple syrup (not maple-flavoured sugar syrup or syrup from companies that use formaldehyde to harvest their syrup);

1/10 teaspoon cayenne pepper;

and 1 cup (8 fluid ounces) purified or spring water

Detox

Can a semi-fast of raw carrots and water, or juice only, or vegetables without meat really get rid of toxins and help with weight loss?

Detox diets are based on the idea that the body builds up a store of chemicals, toxins, fats and other undesirables, and that the stuff can be flushed out - and weight lost - with certain eating and drinking regimes. It's thought that there are more than 200 of these diets, and as many books, including Carol Vorderman's Detox for Life and Dr Joshi's Holistic Detox.

The diets ban or encourage a wide range of foods. Users claim big improvements; skin glows, hair becomes glossier, and bloating, tiredness and headaches are said to disappear with the pounds. But scientists are sceptical, pointing out that the body does its own detox very effectively. They suggest that any benefits are down to the loss of weight and a switch to a healthier diet. Less bloating, say, is the result of eating less; fewer headaches is the result of cutting alcohol and caffeine; and shinier skin results from better hydration.

"The suggestion that the elimination of noxious agents is enhanced is categorically unsubstantiated and runs counter to our understanding about human physiology and biochemistry," says Professor Roger Clemens, who has investigated the diets at the University of Southern California. "Healthy adults, even overweight adults, have been endowed with extraordinary systems for the elimination of waste and regulation of body chemistry. Our lungs, kidneys, liver, gastrointestinal tract and immune system are effective in removing or neutralising toxic substances within hours of consumption."

The American Institute for Cancer Research is also sceptical: "For some, a short-term detox diet could be safe, and perhaps spiritually beneficial, but no sound research documents any health benefits. The weight loss people report is probably temporary, since it comes from fluid losses, not body fat melting away."

Diet another day

For three years, Dr James Johnson and his colleagues have been losing weight by eating whatever they like - every other day. In the first three months, he shed 35lb. His team from Stanford and New Orleans universities also report signs of improved health and possibly increased lifespan.

The team say the diet, which involves eating as normal one day, then restricting calorie intake the next by 20 to 50 per cent, can affect conditions as diverse as asthma and heart disease. "We have seen improvements in a variety of disease conditions, starting within two weeks, including insulin resistance, asthma, seasonal allergies, rheumatoid arthritis, osteoarthritis, infectious disease, periodontal disease and cardiac arrhythmias,'' says Dr Johnson.

"For three years, we have experimented with an alternate-day pattern of eating. This... appears to have health-promoting effects in the absence of weight loss." 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.