A milestone in the effort to halt the effects of ageing was passed thanks to a study that reveals how genetic activity in the body waxes and wanes over time. Using mice, scientists have profiled specific genetic changes over a lifetime, providing a genetic map of ageing. They discovered that the activity of a handful of genes changed markedly with age, notably those involved in stress responses, protein repair and energy production. Moreover, they reveal how a low-calorie diet works at the most basic level to extend life span and preserve health, suggesting that such a diet hinders ageing by slowing metabolism and reducing stress responses. Such knowledge promises to help the development of drugs that mimic the age-retarding effects of a low-calorie diet.

Some 10 per cent of the mouse genetic code, or genome, was surveyed using a "gene chip" - a small glass plate containing DNA that, when read with a laser, reveals the activity of thousands of genes. The team charted changes in genetic activity in two groups of mice, one on a standard diet and another on 76 per cent of the standard diet.

With age, the activity of a small number of genes - less than two per cent of those surveyed - changed markedly. Those genes governed critical biological tasks and they changed in big ways. At the molecular level, normal ageing looks like a state of chronic injury. But those same genes remained intact in mice on a reduced diet. This is a leap in our understanding of how caloric restriction works. There hasn't been much consensus on how caloric restriction retards ageing.

Over many years, studies of several animal species have consistently shown that by reducing diets by 25 to 30 per cent, ageing is retarded and life span extended. The new study tends to support the idea that calorie restriction works by slowing metabolism. In the process of metabolism, toxic by-products are produced, damaging proteins and triggering a stress response that acts to repair damaged molecules. But with age, he added, the body's ability to repair damaged proteins declines, possibly as a result of shrinking cellular energy levels.

Science August 1999

COMMENT: There seems to be a compelling amount of support for reducing the number of calories that we eat if our aim is to have a long life. This new information uses some of the highest technology that biological science now has to unravel some of the mechanisms of how this might occur. There are other methods that one can reduce the stress response. Prayer is probably the most powerful, but exercise, deep breathing and many other regularly applied disciplines will facilitate this powerful benefit of lowering stress hormones, such as cortisol.