This powerful statement is among the most important findings made by research doctors Weindruch and Walford, based on the hundreds of animal experiments which they have conducted involving dietary modification and restriction (see Chapter 5). And, what is more, they believe that what they have found is available to all of us by simply applying the principles they have established from their studies.

As well as this, they point to another phenomenon, and that is that animals already ill with chronic disease at the start of the dietary restriction experiment frequently recovered full health, with the illness significantly improving or vanishing completely. They explain that a number of diseases arise 'spontaneously' (it might be more accurate to say they commonly arise, since they do not appear in everyone there is obviously a cause, and this cannot therefore be considered spontaneous) in humans as they age, including cardiovascular disease, cerebrovascular disease, cancer, diabetes, arthritis, osteoporosis, dementia, cataracts etc. Some of these are clearly life-threatening, adding markedly to the likelihood of a reduced life span, while others increase the chances of accidents as well as reducing the quality of life.

The animal studies that the two researchers conducted showed that not only are these diseases far less likely to occur when diet is modified, but that if they do occur it will be at a far later stage in the life of the animal. Thus 'spontaneous' diseases of old age are reduced in animals that live on a diet which contains a full complement of nutrients (vitamins, protein etc.) but which has a lower than usual level of calorie content.

A longer life, less chance of developing serious disease and even recovery from such disease if it already exists. These are quite astounding and revolutionary claims.

Different patterns of dietary restriction
The ways in which animals are induced to achieve a restricted diet varies. In some instances they are allowed to eat whatever they wish of a fully balanced diet for a restricted amount of time; often this is for 12 hours every other day. In other instances they are fed a known amount of food which represents between 40 and 70 per cent of what similar animals would eat when offered the chance to feed whenever they wish. In some experiments these restricted amounts are boosted by supplements of nutrients to ensure that no deficiencies occur. Diets which contain an identical amount of nutrients (apart from calories) to those given to non-restricted animals are called isonutrient diets.

The animals were started on a restricted diet both very early in life, and later in life to compare the effects brought about by early and late changes. In each case the diet, when used experimentally, produced similar results in increased life span and reduction of disease, but it was found that when the diet restriction was started early in life it could have particularly harmful side effects through changes in the development of the animal, unless nutrient intake was kept at levels of absolute excellence.

These two research pioneers say that they decided to introduce adult animals to dietary restriction with the express purpose of learning more about the improvements in the disease patterns commonly seen in human ageing. Such eating patterns, they believe, can plausibly be usable in humans. But, in responding to the two searching questions which they had posed-'Can adult dietary restriction slow down the onset of late-life disease in humans? and 'Can human adult dietary restriction forestall the progression of, or aid in curing, ongoing diseases?' - their answer included what can only be a mistaken assumption because they said: 'Although human data are unavailable, results of adult dietary restriction studies in rodents, although much less extensive than early life dietary restriction studies, also show favourable effects on late-life disease patterns.'