Protein shortens life but leads to more children

The key to longevity is eating less protein - and not just fewer calories, as has previously been thought - scientists have discovered. But the catch is that while cutting protein may help you live longer, it may mean you'll have fewer children.

"Animals that eat less live longer - up to a point," says Professor Stephen Simpson of the University of Sydney's School of Biological Sciences. "Our research using animal models shows the balance of protein to carbohydrate in the diet is critical."

The idea that restricting food intake without malnutrition prolongs life has become a core belief in gerontology research, Professor Simpson says. "We know dietary restriction extends life in yeasts, fruit flies, worms, mice and monkeys, and it is widely held that the same affect should be true for humans."

But scientists couldn't be sure whether it was the restriction of calories in itself, or the restriction of specific nutrients, that affected ageing. But now Professor Simpson and colleagues at Seoul University, Auckland University, UNSW and Macquarie have measured for the first time in any organism the relationship between diet, nutrient intake, lifespan and reproduction

Using new techniques developed by Professor Simpson and Professor David Raubenheimer (Auckland) the team showed in the fruit fly that calorie restriction is not responsible for extending lifespan: rather the balance of protein to carbohydrate in the diet was critical

"Flies lived longest when the diet contained a low percentage of protein, and died sooner the more protein they consumed," says Professor Simpson. "But protein is needed for reproduction - so flies are faced with a conundrum: eat less protein and live longer, or eat more protein and lay more eggs?"

Professor Simpson said his team 'asked' the flies what they preferred. "When offered a choice, flies behaved like nutrient-seeking missiles, unerringly mixing a relatively high protein diet that maximised their lifetime egg production. In other words, flies preferred to achieve maximum evolutionary fitness rather than live as long as possible."

"In demonstrating the role protein plays in determining both lifespan and reproduction, my co-authors and I have united a body of apparently conflicting work within a common framework and provided a new platform for studying ageing in all organisms," Professor Simpson said.

The research has just been published online in PNAS (Proceedings of the National Academy of Sciences of the United States of America).

http://www.usyd.edu.au