But are these approaches really applicable to humans?
Two of the major researchers into the effects of dietary restriction on life extension are Richard Weindruch Ph.D. and Roy Walford MD (the former is a researcher at the National Institute of Health, Bethesda, Maryland, and the latter a professor of pathology at the University of California, Los Angeles).

They say: 'We think that there is a very high order of probability that animal data are translatable to humans, in terms of retardation of ageing and life span extension as well as disease prevention.' (The Retardation of Aging by Dietary Restriction, Charles Thomas, Springfield, Illinois, 1988).

Can we assume that animal studies are relevant to humans?
Much of the evidence which has been accumulated in support of life extension through dietary modification involves animal experimentation, but a noted expert, Sir Kenneth Blaxter (writing in the Journal of Nutrition and Reproduction International, 1979) said: '. . . the conclusion seems to be inevitable that the proper species to use in the study of the nutrition of man is man himself.'

For conclusive results of the effects of diet on longevity in humans, with the purpose of proving or disproving the animal evidence gathered to date, a study would need to run for about 100 years, and would require absolute adherence to the diet being tested. This is just not possible. So, to be practical, it is necessary to look for options which are within our reach.

Can we believe animal study evidence at all?
To answer this question we need to look at three things. First we must ask whether we should even honour such experimentation by quoting it, giving it credence, and taking note of its findings. Second, if we can get past these doubts, we must be reasonably sure that the results are also applicable to humans, before we try to use the findings. Third, we must look for alternatives - cell cultures, for example, and evidence from humans who have for many years followed patterns of diet which approximate in some way to the animal studies.

Leaving aside the question of applicability to the human condition, there is a rising tide of feeling against viviSsection (physical experimentation on living animals). However, insofar as life extension experiments are trying to find ways of prolonging the lives of the participant creatures it can be argued that what is being done is in direct contrast to the normal fate of experimental laboratory animals, where life span tends to be shortened rather than lengthened. I accept, though, that even this argument would not convince someone who abhorred animal experimentation on moral grounds, whatever the comfort of the animals, or any positive outcomes their might be, or even the importance of the information gathered in this way.

However, many believe that since the experiments quoted have already been carried out, and since the evidence is of importance to a great many people, we should make ourselves aware of the results, without necessarily condoning the methods used.

Alan Hipkiss Ph.D. and Alan Bittles Ph.D., writing in Human Aging and Later Lik (edited by Anthony Warnes Ph.D. and published by Edward Arnold, London, 1988), have their own views on the subject:

Given that dietary restriction is the only factor known to increase longevity in any animal model, and given its inapplicability to the human condition, one must question whether information appropriate to human ageing can be obtained from animal models. On the other hand, animal studies obviously have their place in comparative research programmes into ageing.