Key To Healthy Long Life Could Lie In Balancing Protein Intake Rather Than Calorie Restriction

05 dec 2009--UK researchers studying flies suggest that balancing protein intake rather than reducing calories may be the key to healthy ageing; their findings may explain why calorie restriction, cutting down food intake while making sure the diet contains enough vitamins, minerals and other essential nutrients, appears to benefit health, and also in some organisms, to increase longevity.

The study is the work of Dr Matthew D W Piper from the Institute of Healthy Ageing in the Department of Genetics Evolution and Environment at University College London, and colleagues, and a paper on it appeared online on 2 December in the journal Nature.

Previous research suggests that calorie or dietary restriction, reducing food intake while making sure the diet contains enough vitamins, minerals and other essential nutrients, causes many organisms, including mice, rats, Rhesus monkeys, and fruit flies (drosophila) to live longer and with better health.

There is also evidence that calorie restriction results in greater health in humans too, but whether it increases our lifespan is not so clear.

But there is a downside: dietary restriction diminishes fertility: a female fruit fly on a calorie restricted diet reproduces less frequently and when she does, she produces fewer offspring, although her reproductive span is longer.

The researchers suggest this is an evolved survival trait; when in short supply, essential nutrients are diverted from supporting reproductive systems to keeping the organism alive.

The UCL Institute of Healthy Ageing researchers wanted to investigate this in more detail: was it calorie restriction per se that led to increased health benefits, or was it the effect of reducing specific nutrients?

For the study, which was funded by the Wellcome Trust and Research into Ageing, Piper and colleagues observed what happened when they fed female fruit various diets comprising yeast, sugar and water, but with different amounts of essential nutrients such as vitamins, lipids and amino acids.

They found that varying the amounts and proportions of amino acids in the diet affected the lifespan and fertility of the female fruit flies, but there was little or no effect when they varied the other nutrients.

On closer investigation they found that the amino acid methionine was crucial to extending lifespan and reducing fertility: when they added it to a low calorie diet it boosted fertility without reducing lifespan, and curiously, when they reduced it in a high calorie diet it extended lifespan.

Piper told the press that:

"By carefully manipulating the balance of amino acids in the diet, we have been able to maximise both lifespan and fertility."

"This indicates that it is possible to extend lifespan without wholesale dietary restriction and without the unfortunate consequence of lowering reproductive capacity," he added.

Piper explained that in the past we thought it was the amount of protein in the diet that was important, but this study shows that in flies, and he suggests this is likely to be the same for other organisms too, the balance of amino acids can affect health later in life.

"If this is the case for humans, then the type of protein will be more important," said Piper, explaining that it is not simply a case of telling people to eat more or fewer nuts to live longer, "it's about getting the protein balance right, a factor that might be particularly important for high protein diets, such as the Atkins diet or body builders' protein supplements".

Although the fruit fly does not look like a human, and we have about four times the number of genes that they have, many of the discoveries about how fly genes behave can often be matched against human couterparts.

Dietary restriction appears to be an evolutionary trait, occuring in organisms from yeast to monkeys, suggesting these mechanisms are preserved in genes that we all have in common, or that have largely similar properties. This opens the possibility of using organisms like the fruit fly to study how dietary restriction works and to translate that into the human equivalent.

Amino acids are the building blocks of life: they make up proteins, complex organic compounds that take part in nearly every process necessary for keeping an organism alive. Methionine is an important amino acid because it is essential to the formation of all proteins.

Proteins are made naturally in the body, and we also source them from a variety of foods, including meat, dairy, nuts, pulses and soya derivatives like tofu.

Methionine occurs in naturally high levels in foods such as sesame seeds, Brazil nuts, wheat germ, fish and meats.

"Amino-acid imbalance explains extension of lifespan by dietary restriction in Drosophila."
Richard C. Grandison, Matthew D. W. Piper & Linda Partridge.
Nature, Published online 2 December 2009
doi:10.1038/nature08619