The findings support the theory that as the body grows old it is less able to repair the damage caused by a gradual build-up of toxic by-products, such as highly active "free radicals" produced during chemical oxidation within the cells.
It is thought that restricting calorie intake, provided that other nutrients are taken at normal levels, slows down the production of these toxins, thereby delaying the ageing process.
Some genes are likely to be responsible for mopping up the toxins before they do much damage. The latest research is a way of identifying these genes, which could possibly lead to developing new drugs to augment their activity.
Calorie restriction appears to delay the onset of ageing in part by interfering with the way genes are switched on or off as people get older, the researchers believe.
By studying changes in the activity levels of about 3,400 genes in laboratory mice fed on a low-calorie diet, the scientists found that a small percentage of these genes played a direct part in determining lifespan.
The scientists believe that the work could open the way to new insights into human ageing and how it can be slowed down by changes in diet and lifestyle, which could have a direct influence on some genes.
Previous work on rats has indicated that caloric restriction - where the diet has up to 30 per cent fewer calories but normal nutrient levels - can significantly extend lifespan, although there has not been any direct evidence yet that the same is true for humans.
The latest study by Tomas Prolla, professor of genetics, and Richard Weindruch, professor of medicine, at the University of Wisconsin-Madison demonstrated that about 2 per cent of the genes studied were affected by ageing. The genes appear directly to influence the body's response to such age- related things as stress, tissue repair and energy production.
"This study has analysed more genes with regard to ageing than all previous studies combined," Professor Prolla said. "At the molecular level, normal ageing looks like a state of chronic injury."
Half the mice in the study - published in the journal Science - were placed on calorie- restricted diets from an early age and their genes showed just how the animals adapted to the reduced intake of energy.
"This is a big leap in understanding how a reduced-calorie diet works. There hasn't been much consensus on how calorie restriction retards ageing," Professor Weindruch said. "We now know which sets of genes that change with ageing are affected by caloric restriction. We think this technology has led us to a panel of molecular markers of ageing which will enable use to screen panels of potential anti-ageing drugs."Reuse content