Calorie-restricteddiets could be the secret to a longer life. Ayala Ochert,reporting on the latest research, finds out that less really is more.
At long last, the secret to a long life is out - but it is a bitter pill to swallow. The fact is, there is no pill, you just have to diet every day for the rest of your life. The euphemism scientists use is "calorie restriction", but it means nothing more than eating less, while making sure that you get the right amount of vitamins, minerals and other nutrients.
Actually, calorie restriction is not much of a secret - experiments on animals have for years shown that such a diet not only prolongs life, it also reduces the risk of age-related diseases like diabetes and cancer. But Roy Walford, professor of pathology at the University of California, Los Angeles, now presents the best evidence to date that it does the same for humans.
In the early 1990s, Walford took part in the Biosphere 2 project. Along with seven others, he lived and worked in a controlled environment, sealed off from the outside world in a space of seven million cubic feet, eating a carefully controlled and calorie-restricted diet. As physician on the experiment, Walford took regular blood samples from each of his colleagues.
"All the physiological effects that we saw in animals were duplicated in humans, so we can assume that the other effects will also be duplicated - increased lifespan and increased resistance to disease," says Walford, who found a considerable drop in blood pressure, cholesterol, insulin and glucose in the calorie-restricted participants. Of course, they also lost a lot of weight, the men weighing 18 per cent less than before and the women 10 per cent less.
The lifespan of rodents put on a severe diet is extended from 38 to 56 months, which for a person is equivalent to living to be 160 years old. But despite the apparent austerity of such a lifestyle, a group of dedicated individuals have been following it, some for over a decade, collecting data about themselves in what Walford calls the "first scientific experiment organised largely by lay people and conducted on the internet". Their results have been similar to Walford's Biosphere 2 experiment as well as similar experiments involving monkeys.
Although any amount of calorie restriction is considered beneficial, Walford recommends finding your own natural "set-point" - the weight you tend to hover around - and then gradually reducing calories until you are 15 to 20 per cent less than your set-point. Calorie-restriction is then used to maintain this lowered weight.
Walford is disparaging of those who say that living a life on a diet is hardly living at all. "Look at vegetarians. A lot of people say they couldn't live without meat, but vegetarians don't live deprived lives," he says. "It depends what you want to optimise - feeling really well, being physically active, needing less sleep - or you could say, 'I can't live without my angel-food cake'. It's a balance, a trade-off." And he warns that these results can only be achieved through eating less - excessive exercise may cause weight loss but it could promote ageing. "The question now is what is the mechanism? If we knew that, then perhaps we could bring about the same effect without having to starve ourselves," Walford says.
Steven Spindler, professor of biochemistry at the University of California, Riverside, has been looking at levels of "chaperone" proteins. "Chaperones, as their name suggests, encourage appropriate interactions between proteins," he explains. He has found that a calorie-restricted diet reduces the levels of chaperones, which in turn increases the chances of apoptosis, a kind of cell suicide. Apoptosis is a normal process that cells go through and is an important defence against cancer. So this change in chaperone levels could explain why a calorie-restricted yet nutritious diet reduces the risk of cancer, says Spindler.
Despite the plausibility of such mechanisms, researchers are no nearer agreeing on a theory of ageing. "The trouble is that our results correspond to every theory of ageing that there is," Walford says. "(Eating a calorie-restricted diet) increases the rate of DNA repair, it decreases free radical damage, and it preserves immune capacity into old age."
Those of us not yet ready to give up chips for life may be looking to modern genetics for the promise of a longer life. When the Geron Corporation announced last year that it had found a way of keeping cells dividing indefinitely, speculation ran rife about the possible applications for substantially prolonging our own lives.
Left to their own devices, cells will divide a certain number of times and then stop. This "cell ageing" is considered by some to be a model of ageing in general, but Steve Austad of the University of Idaho is not so sure. "When Geron found a way of turning on telomerase at will so cells keep dividing, there was a huge amount of hype, most of it not generated by the scientists," he recalls.
When a normal cell divides, sections at the ends of chromosomes - telomeres - shorten a little. When they get to a certain critical length, cell division stops. But Geron researchers used the enzyme telomerase to arrest this process and allow cell division to go on unabated.
"What we've done is gone back one step, and we've found that all the evidence of this relation between cell division and ageing is unravelling. There is no relation," Austad claims. Cells from young people had been found to divide more times than those from old people. But his own study, which involved only healthy people of all ages, concludes that there is no relation between age and the number of cell divisions.
"There is very little evidence that anything in ageing has anything to do with cells dividing. The main problem in ageing is unwanted cell division, like you see in cancer, not the lack of cell division," Austad concludes. So for the foreseeable future, it seems that eating a bit less is the only way to live a bit longer.