Is fasting a free health fix – or is it just a fad?

Restricting the amount you eat is said to fight disease, extend lifespan and improve wellbeing. As well as dieters, people with diabetes and MS could benefit

You probably first came across it with a pale-looking colleague slumped over their office desk. Or with The Fast Diet author Michael Mosely speaking effusively about it on television. Fasting, they’d have told you, is a great way to lose weight. It makes sense: eat fewer calories a couple of days a week, and don’t overeat on the others, and you’ll slim down. What’s less clear is the assumption that fasting from time to time can bring other benefits such as avoiding disease, keeping your brain sharp and even letting you live longer. With all this for the price of just a sprinkle of willpower though, surely it’s all too good to be true?

The answer is not straightforward. Perhaps unsurprisingly, the evidence is strongest with type 2 diabetes – a disease often caused by overeating. The disease means that a person can no longer control their blood sugar levels. Once diagnosed they are left staring down the barrel of a lifetime on medication, unless, think researchers at Newcastle University, they begin to fast.

They’ve tested an extreme low-calorie diet – a hunger-panging 600 calories a day for eight weeks – in 11 people with type 2 diabetes: all were disease-free by the end of the fast; seven were still disease-free three months on. Later studies suggest that the sooner people fast, the better their chances of reversing their disease. Roy Taylor, who leads the group, thinks that fasting is beneficial because it gets rid of dangerous fat in and around your organs, including two that are important in sugar control – the pancreas and the liver.

When an otherwise healthy person’s blood sugars get too high, their pancreas makes a hormone called insulin that tells the liver to remove the sugar and store it safely. “If you have fat around these organs it clogs up the way they work and your body can’t control its blood sugars,” says Taylor. After about 12 hours of fasting, he says, the body uses up all the glycogen in the liver, its go-to source of energy, and starts to dip into its fat deposits. “The first type of fat to go is that dangerous fat around the organs, freeing them up to do their job properly.” He stresses that people with diabetes should not fast without consulting their doctor – a combination of insulin drugs and fasting can be lethal.

Taylor and his colleagues are now testing their fasting diet in around 300 people with type 2 diabetes. The results of that study will give a better idea of how beneficial the diet can be. The question is how much of the effect is down to fasting and how much is down to just the weight loss? “It’s almost certain that other forms of dieting will do the same,” says Taylor. “But this low-calorie diet is one that I was confident would let people lose the roughly two and a half stone, or a sixth of their body weight, that we were looking for.”

There is, though, reason to believe that fasting might have benefits over and above weight loss. It’s down to what happens to all living organisms when they don’t have food – they begin to eat themselves. Gruesome, maybe, but it’s beneficial: it lets the body recycle energy and do some housekeeping – the first cells to go are the faulty ones.

Valter Longo is a scientist at the University of Southern California who believes that, because of this process, periodic fasting can help people stay healthy. Faulty immune cells, for instance, could be pruned back so that when a person starts to feed again, new cells are spawned from only the strongest and the fittest.

In experiments in mouse models of multiple sclerosis, a disease in which rogue immune cells erroneously attack a person’s nerve cells, he’s seen that periodic, low-calorie fasting can slow down the destruction of cells and even lead to some regeneration. His preliminary work in people with the disease suggests it could improve their quality of life.

The potential reaches further. Fasting-mimicking diets can help people with cancer undergoing radiation chemotherapy, presumably by promoting the growth of healthy cells and restricting the growth of cancerous ones. Restricting the amount a mouse eats by about 30-40% can extend its lifespan by a third.

This year Longo showed that a fasting-mimicking diet could help mice with diabetes regain blood sugar control, not only those with type 2 but also those with type 1 diabetes, caused not by overeating but by a faulty immune system. The benefits, he says, were down to a reprogramming of beta cells, a type of cell in the pancreas that makes insulin. He also starved cells taken from people with type 1 diabetes and saw a similar reprogramming.

“These results are surprising and completely new territory,” warns Gordon Weir, a diabetes researcher at Harvard Medical School. “I’d be cautious about assuming that fasting will help people with type 1 diabetes until the mouse studies are replicated in other laboratories and it has gone on to be shown to work in human beings, not just in human cells.”

Longo, too, is wary of giving false hope but is bullish about the potential of fasting. “In research over 25 years we’ve seen it in E coli bacteria, in yeast, in human cells, and in mice,” he says. “The foundations are so deep that it’s as old as life itself, but we have to respect the complexity – a yeast is a yeast, a mouse is a mouse, and a person is a person.”

The difficulty in transferring a theory from mouse to man is that people live much longer than mice. At middle age we are much farther from when our stem cells, the type of cells that make other cells, are most active, so our ability to generate new cells might not be as strong.

“We don’t have conclusive data that any of this works in humans,” Longo says, “but we do have some promising data.” He’s referring to a study of 100 generally healthy people given a fasting-mimicking diet low in calories, sugars and protein but high in unsaturated fats. Despite only a minor reduction in weight loss, he says, risk factors for ageing, diabetes, cancer and cardiovascular diseases such as heart attack and stroke were all improved. He’s planning a bigger trial in 250 people to confirm these findings and to figure out which benefits are the result purely of the act of fasting and not just the result of weight loss.

Other tests will take a little longer. Whether fasting will ever make us live longer, given the time needed to prove it, will be for only Dracula and Dorian Gray to know. What could be more compelling is the idea that fasting can keep us in better mental shape.

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