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You are what you eat – so does eating old food make you old? It sounds far-fetched, but experiments on mice, flies and yeast suggest that it might.

The fundamental causes of ageing aren’t well understood. A leading idea is that throughout life, our bodies accumulate cellular damage. That might include oxidative damage to cells caused by by-products of aerobic respiration, and DNA damage – or a combination of those and other types.

at Harvard University wondered whether organisms might also be able to acquire cellular damage from their food.

Food is broken down and used as the building blocks for many cellular processes, so eating older organisms – which have more molecular damage themselves – might cause an animal to age faster than one that eats younger organisms with less molecular damage.

To test the theory, Gladyshev and his team grew yeast fed on culture media made from old or young yeast and fed fruit flies food made from old or young flies. They also studied mice fed meat from old or young deer. The animals were fed their particular diet from early adulthood for the rest of their lives.

The old diet shortened lifespan by 18 per cent in yeast and 13 per cent in flies. In the mice, the old diet shortened lifespan by 13 per cent in female mice, but there was no significant effect among males.

Ageing food

Gladyshev thinks that they may see an effect in both sexes if they increase the sample size – and believes the results seen in yeast, flies and female mice support his hypothesis.

at the University of Liverpool in the UK isn’t so sure. He thinks the results could be explained by broader nutritional differences in the composition of old and young meat, rather than molecular damage linked to ageing. “There are different nutrients in the tissues from old animals and young animals,” he says. “Lamb doesn’t taste like mutton.”

Gladyshev’s team tried to control for this in the mouse diet by ensuring the old and young diets had similar quantities of fat, carbohydrate and protein. But Gladyshev admits that they couldn’t ensure everything was the same. “This also could be a factor,” he says.

Whatever the reason, we shouldn’t draw any conclusions about human nutrition from the findings, Gladyshev says. There was only a small effect on animals fed on old animals for their entire lives; people don’t tend to eat old animals and our diets are more varied.

Instead, the secret to staying young may be to alter our metabolism in ways that reduce the overall damage we accumulate. Calorie restriction and the drug rapamycin, two approaches currently being studied for their life-extending propensities, might work in this way. “I think there could be many ways to extend lifespan,” says Gladyshev.

De Magalhaes thinks molecular damage isn’t the whole story. Some aspects of ageing may be written into the programme of our development. “We don’t know exactly why we age – there is evidence pointing to a combination of molecular damage, but also other programme-like mechanisms at play,” he says.

Read more: Everyday drugs could give extra years of life; Calorie restriction diet extends life of monkeys by years; A cure for ageing is near but you probably can’t afford it