I would strongly refute the statement that dietary restriction methods are 'inapplicable' to the human condition for, as we will see in the chapters that follow, a number of strategies allow us to incorporate aspects of the methods used in these animal studies into our lives if we so choose. I also confess to confusion when told in the same paragraph that animal studies are and aren't useful as evidence. Certainly Walford and Weindruch take a very different position as to the value of information to be gained from animal research. And they are supported by the views of one of the great nutritional pioneers of this century, Sir Robert McCarrison.

Some of his most important research focused on the various dietary patterns followed by different ethnic groups living on the Indian sub-continent, and he found that in feeding these similar patterns to rats that he could produce amazing confirmation of the effects of their diets on the health, physical size and longevity of the different groups. He tells us of these experiments and the results in his remarkable monograph Nutrition and Health (republished by the McCarrison Society, 76 Harley Street, London W1 in 1982 having first been published by Faber and Faber in 1943):

. . . the frequency with which results observed in rats are applicable to man is remarkable - a fact which will be the better appreciated from the examples which I will place before you. Without such experiments on animals the vast amount of knowledge revealed by them would be hidden from us and we would stiJ1 be in ignorance of the kind of consequences to expect in man from his continued use of food of faulty constitution. We would, moreover, be in ignorance of what a properly constituted diet is.

P. Vincent Hagerty Ph.D. of the University of Minnesota, writing in Contemporary Nutrition (March 1981), states that choice of animals for experiments is often dictated by convenience and economics rather than sound biological principles. He points to varying results in nutritional testing involving humans and specific animals, and even between different strains of the same animals. He also questions the care with which other factors such as stress are considered when nutritional tests are conducted, especially in relation to rats. However he concludes that: "The contribution of animal models to understanding alterations in biochemical and physiological processes in complete nutritional stresses has been invaluable."

If precautions are taken regarding selection of species, strains, diet, duration of experiments, adaptation to the diet and a variety of other criteria, useful information can be derived. The choices open to scientists seeking the secrets of prolongation of life seem to fall into three possibilities:

• To use animal studies

• To try to deduce evidence from human experiments (difficult but not impossible)

• To use human tissue (cells) in culture dishes to see what happens to them over time and under different conditions.

It is towards the last of these choices which some researchers are moving, since it is now known that when cells are carefully cultured, in laboratory settings, providing that they are ensured optimal conditions and nutrients, they continue to divide and reproduce for a predictable number of times until they begin, of their own volition, to age.

As Drs Bittles and Hipkiss put it: 'The fact that human cells derived from the skin or lung, such as fibroblasts, undergo senescence [ageing] in culture shows that ageing has an intrinsic [built in] cellular basis and is not solely a consequence of defective intercellular communication (hormonal influence etc).' Since the cellular changes seen in culture situations are very similar, if not identical, to those seen in animal studies (as well as to those found in the cells of people who have aged normally) it seems reasonable to accept evidence from both sources (animal studies and cultured cells) as a reliable basis upon which to build a picture about this fascinating subject.