The Economist, Article about CR

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Here is an Article from the March 31st edition of the Economist:

Rad

Longevity

All you can't eat

Mar 31st 2005

From The Economist print edition

Even a slight decrease in calories may lead to longer lifespans

MOST people would not object to living a few years longer than

normal, as long as it meant they could live those years in good

health. Sadly, the only proven way to extend the lifespan of an

animal in this way is to reduce its calorie intake. Studies going

back to the 1930s have shown that a considerable reduction in

consumption (about 50%) can extend the lifespan of everything from

dogs to nematode worms by between 30% and 70%. Although humans are

neither dogs nor worms, a few people are willing to give the calorie-

restricted diet a try in the hope that it might work for them, too.

But not many—as the old joke has it, give up the things you enjoy and

you may not live longer, but it will sure seem as if you did.

Now, though, work done by Marc Hellerstein and his colleagues at the

University of California, Berkeley, suggests that it may be possible

to have, as it were, your cake and eat it too. Or, at least, to eat

95% of it. Their study, to be published in the American Journal of

Physiology—Endocrinology and Metabolism, suggests that significant

gains in longevity might be made by a mere 5% reduction in calorie

intake. The study was done on mice rather than people. But the

ubiquity of previous calorie-restriction results suggests the same

outcome might well occur in other species, possibly including humans.

However, you would have to fast on alternate days.

Why caloric restriction extends the lifespan of any animal is

unclear, but much of the smart money backs the idea that it slows

down cell division by denying cells the resources they need to grow

and proliferate. One consequence of that slow-down would be to stymie

the development of cancerous tumours.

Cancer is the uncontrolled growth of cells. For a cancer to develop

efficiently, it needs multiple mutations to accumulate in the DNA of

the cell that becomes the tumour's ancestor. To stop this happening,

cells have DNA-repair mechanisms. But if a cell divides before the

damage is repaired, the chance of a successful repair is

significantly reduced. A slower rate of cell division thus results in

a slower accumulation of cancer-causing mutations.

At least, that is the theory. Until now, though, no one has tested

whether reduced calorie intake actually does result in slower cell

division. Dr Hellerstein and his team were able to do so using heavy

water as a chemical " marker " of the process.

Heavy water is heavy because the hydrogen in it weighs twice as much

as ordinary hydrogen (it has a proton and a neutron in its nucleus,

instead of just a proton). Chemically, however, it behaves like its

lighter relative. This means, among other things, that it gets

incorporated into DNA as that molecule doubles in quantity during

cell division. So, by putting heavy water in the diets of their mice,

the researchers were able to measure how much DNA in the tissues of

those animals had been made since the start of the experiment (and by

inference how much cell division had taken place), by the simple

expedient of extracting the DNA and weighing it.

Dr Hellerstein first established how much mice eat if allowed to feed

as much as they want. Then he set up a group of mice that were

allowed to eat only 95% of that amount. In both cases, he used the

heavy-water method to monitor cell division. The upshot was that the

rate of division in the calorie-restricted mice was 37% lower than

that in those mice that could eat as much as they wanted—which could

have a significant effect on the accumulation of cancer-causing

mutations.

But calorie-reduction is not all the mice had to endure. They were,

in addition, fed only on alternate days: bingeing one day and

starving the next. There were two reasons for this. First, bingeing

and starving is how many animals tend to feed in the wild. The

uncertain food supply means they regularly go through cycles of too

much and too little food (it also means that they are often

restricted to eating less than they could manage if food were

omnipresent). The reasoning here is that metabolic processes evolved

in a particular context and might be expected to work best in that

context. Replicate the evolutionary context and you might get a

better outcome.

The second reason, according to Elaine Hsieh, one of Dr Hellerstein's

colleagues, is that cutting just a few calories overall, but feeding

intermittently, may be a more feasible eating pattern for some people

to maintain than making small reductions each and every day.

Whether modern man and woman, constantly surrounded by food and

advertisements for food, would really be able to forgo eating every

other day is debatable. But even if it does work (and Dr Hellerstein

has yet to prove that reduced cell division translates into longer

life) the temptations of life may prove just too much for wannabe

Methuselahs