There is no question whatever that dietary restriction tactics lengthen life and reduce disease incidence in species after species of animals that have been tested, and there is no reason whatever to suppose that this will not also apply to humans. Indeed, there is strong evidence already available that says it does so.
Many investigators believe that dietary modification does not lengthen life unnaturally, but rather that it allows humans and animals to reach something close to their normal potential life span; although there remains some controversy over what is and what is not ‘normal’. Some argue that since the life expectancy of animals in the wild is shorter than that achieved under ‘ideal’ laboratory conditions, what the experiments are achieving is an extension beyond the natural term. However, another way of looking at it would be to say that if optimal conditions prevailed in the wild (adequate food and no dangers from predators and climatic extremes, for example), this would be even more ‘natural’ than laboratory conditions, no matter how ideal, and would probably lead to enhanced life spans so far achieved only under laboratory conditions.
What happens in the laboratory cannot be thought of as natural, but the results obtained surely point to ways in which everyday life and habits might be modified to produce the benefits of a longer, healthier life. It is, after all, hardly natural that we purify our drinking water. In just this sort of way modifications to our eating patterns might become the norm, and while seemingly ‘unnatural’ such changes might allow our true potential to emerge.
Places where restricted calories (and longevity) am the norm
Several population groups have long been reputed to be remarkably long-lived. These include the South American people of Vilcabamba, the central European Caucasian peoples and the Hunza people of the Himalayas. Apart from all being resident in inhospitable mountainous regions their diets seem similar in a number of respects, including the central issue of being lower in overall calorie content than ‘normal’ (usually around half that normally consumed by active adults in Europe and the US – 1,600 to 1,900 calories per day as against 3,300 for US males of all ages).
The truth of the claims of longevity of such populations is, admittedly, open to doubt, owing to the lack of well-documented legal records of births and deaths, but there is one population group where this is not the case, and where dietary restriction of calories has long been the norm, with quite startling and well recorded results in terms of longevity and health.
Human evidence from Japan
There exists a near perfect example of dietary restriction in action amongst humans. People living on the Japanese island of Okinawa come very close to living on a diet which fulfill the requirements of dietary restriction, as successfully applied to animals in life extension research, and doctors Weindruch and Walford (Retardation of Aging and Disease by Dietary Restriction, Charles Thomas, Springfield, Illinois, 1988) examined a particular group in detail in order to compare them with the studies they had conducted on animals. The evidence they accumulated is compelling.
There are excellent and accurate legal records of births and deaths on Okinawa, which have been kept since 1872, and this allows us to know exactly how long people are living. We are also fortunate that for many years the Japanese Ministry of Welfare and Health has evaluated the dietary habits of different households, chosen randomly, in all areas of the country. This provides us with another useful source of information as we compare the life expectancy of one group against another, especially as it is now known that the people of Okinawa produce centenarians up to 40 times more often than do other Japanese population groups.
Japan has for many years been known to have a long-lived population, compared with the rest of the world, and yet Okinawa does far better than the country as a whole. For example:
- Out of every 100,000 people in Japan aged between 60 and 64 2,180 die each year on average, whereas in Okinawa only 1,280 out of every 100,000 people of that age die annually.
- For every 100 people who die each year from strokes in Japan only 59 die in Okinawa.
- For every 100 people who die from cancer in Japan each year only 69 die in Okinawa.
- For every 100 people who die from heart disease in Japan each year only 59 die in Okinawa.
The people of Okinawa also seem to be particularly resistant to auto-immune diseases, and research indicates that this is not because of specific local genetic traits but rather that in these people the common human potential for longevity is given an opportunity to show itself through an overall better level of health.
What do they eat in Okinawa?
The following table compares food intake in Okinawa with that in the rest of Japan.
The energy (calorie) consumption of schoolchildren in Okinawa is only 62 per cent of that of the rest of Japan, at around 1,300 calories daily. This feature of low calorie intake in children closely matches the early-life dietary restriction regimes applied
Fish (and other meat proteins)
Total protein and fat intake
Energy intake (calories)
Okinawa intake as percentage of Japanese intake
to such good effect in some animal studies into life extension. Obviously factors other than diet are also contributory to long life amongst the peoples of Okinawa, such as hard physical activity and an equitable climate, but their general good health and longevity stands as living proof of the benefits that can be gained from a restriction of calories in an otherwise ideal diet.
The evidence from Okinawa is not unique. In 1982 Dr Z. Ho, of the United Nations University, Massachusetts Institute of Technology, published in the Journal of Applied Nutrition (34(1):12-23) his research findings on the diet of very old people in an isolated mountainous region of southern China. He examined the eating patterns of 50 people aged between 90 and 104 (average age 94) which showed that their diets consisted largely of maize, eaten three tunes daily as a gruel, with vegetables and oil. The main vegetable foods eaten included groundnuts, sweet potatoes and rice. Despite this limited range of foods, and a calorie intake well below what is considered adequate by dietitians, the protein intake was considered reasonable at around 10 per cent of their total food intake, averaging between 0.8 and 1.1 grams of protein per kilogram of body weight. None of these old people displayed any signs of vitamin deficiency.
When I come to set out some strategies for life extension later in the book I will look at options which might allow us to translate, into our own lives, aspects of the knowledge which is now on offer, which the people of Okinawa seem to have found, to their benefit, by chance.
Proof from animals
Of the many animal studies which have been conducted, it is the rat studies which interest us most because, as we have seen in Sir Robert McCarrison’s work, the health and well-being of rats follows closely that of humans when fed on very similar diets. In all the major studies of life extension, using dietary modification which incorporates calorie restriction plus full intake of essential nutrients, increases in life span of between 40 and 85 per cent have been achieved. This phenomenal gain in life expectancy has come without negative effects on vitality or health. Indeed, the animals involved usually appear more contented, more alert and vital, than do their free-feeding counterparts.
Dr G. Dewasmes and his colleagues, writing in the Journal of Applied Physiology (49:888) in 1980, describe a natural occurrence of dietary restriction in emperor penguins which highlights the ability of some creatures, in a natural setting, to drastically restrict diet and yet to function at a very high degree of efficiency.
Once these birds leave the sea to find their breeding rookeries on sea ice, sometimes 50 miles or more from the sea, they no longer have access to food (they only feed at sea). Here in the depths of the Antarctic winter they breed, the female laying one egg some 45 days after mating. She then leaves the male to incubate the egg for the next 65 days, while she returns to the sea, reappearing around hatching time. At that time the male walks back to the sea for his first meal in 120 days. He will have lost upwards of half his body weight by this time, but his metabolic rate will have remained normal throughout the fasting but working period.
As with the examples of the people of Okinawa and the host of rodent studies in laboratory settings, we can see that health and vitality do not depend upon an abundance of food in a constant flow. Adequate but optimal nutrition is quite different from our current pattern of eating in industrialized countries, where we see malnutrition combined with over consumption, the very opposite of our aim which should be undernutrition without malnutrition.
An ideal diet for rats
Many different forms of diet have been used in longevity studies involving rats and mice, and over the years more or less standardized formulae have been adopted to achieve an ideal diet for them. However, doctors Weindruch and Walford wisely ask the question: “Ideal for what?”
They point out that an ideal diet for building a large body and maturing quickly is not necessarily an ideal diet for longevity, which should seek to slow down the biological clocks of the animals concerned. We should therefore be aware of these differences, since the modifications to diet which might lead to human longevity would also be less than ideal for anyone seeking to build a Mr. Universe-type body.
Some life extension experiments have been conducted using low protein diets. These do indeed achieve life extension, but nowhere near as effectively as do diets containing adequate protein and all other nutrients, which is fed to the animals either on alternate days or for a limited amount of time each day, leading to between 40 and 70 per cent of the intake that adult animals would eat were they allowed free access to unlimited food. Literally hundreds of studies are cited by Weindruch and Walford which show that dietary restriction tactics applied early on in the life of experimental rodents leads to life extension. However, these approaches usually also lead to stunted growth and delayed onset of puberty, something quite unacceptable in human terms.
It is the studies involving adult onset dietary restriction on rats and mice which are the most relevant to the human condition. Here they found that the best results were achieved when dietary restriction was introduced gradually. In one of their early studies they fed normally long-lived adult rats and mice an isonutrient diet which when fully operational provided just 60 per cent of the calorie intake of control rats which were fed ad lib. An increase in average and maximum life span was achieved of between 10 and 20 per cent, with some mice surviving an extraordinary 47 months.
Further studies have shown that dietary restriction patterns started in early adult life, or even middle age, allows rats and mice to extend their average life expectancy by about 90 per cent as much as would have been gained if the restrictions had started in infancy. This shows clearly that the major drawbacks of delayed puberty and stunted growth, which occur when starting the restricted eating pattern early, can be avoided with negligible loss of benefit by beginning the process later in life.
In these particular studies the longest life span reached by individual mice was 50 months and by rats 46 months. The average life extension achieved in whole groups of mice was 39 months when restriction started as adults, and 43 months when started as infants, as against around 36 months for those animals fed freely throughout life For rats the best average life extension achieved by groups was 35 months for adult onset dietary restriction and 38 months for early onset dietary restriction, as compared with 31 months for those animals fed ad lib throughout life.
When disease prone, normally short-lived animals were exposed to dietary restriction techniques the results were dramatic in reducing the levels of ill-health (auto-immune conditions affecting the kidneys, for example) with the dietary restriction animals showing increased activity and greatly outliving their contemporaries on a normal diet. The implications for humans (see Chapter 4) of such results is stressed by the researchers.
The most recent studies described by Weindruch and Walford involved mice with a tendency towards a variety of late-life tumors. They divided the animals into groups, which began dietary restriction at either 1, 5 or 10 months, as well as a control group in which the diet was not altered. They found that those on unrestricted diets lived an average of 26 months, whereas the various dietary control groups averaged a 31 to 33 months life span. The longest surviving free-fed mouse lived for 34 months, whereas the longest restricted-diet mouse lived for 41 months. They also found that the mice which were started on dietary restriction at one month old did only marginally better than did the adult onset dietary restriction mice.
Don’t overfeed children
Weindruch and Walford point out that efforts to improve life extension, using dietary restriction on adult animals, are more successful with those animals which have not been overfed early in life, before the beginning of the dietary restriction. The animals which do best on dietary restriction patterns of eating, introduced in adult life are those which have matured slowly, and which remain slightly above average weight during the dietary period (indicating energy efficiency) but which had not been above average weight early in life. Being above average body weight did not lead to a longer life if dietary intake remained unrestrained, only if dietary restriction patterns were implemented. From this the message for parents is clear: keep the food intake (and type of food) of children optimal without allowing early obesity to appear.
Pearson and Shaw, writing in Life Extension (Nutri Books, 1983) give their version of why we should take seriously the likelihood that animal experiments such as those outlined above apply to people as well:
Animal studies can be considered relevant to people when: (1) the experiment affects a system in the animal that is like a similar system in humans, and (2) the method of bringing about these changes in the animal involve biochemical pathways (a chain of chemical reactions) found in both people and animals.
Any variations in biochemical activity between an animal species and ourselves would be taken into account when the results of research were evaluated.
Many of the experiments described produce an increase in average (or mean) life span of whole groups of animals (about 75 years in humans) as well as individual extension of maximum life spans (around 120 years in humans) along with a host of health benefits. Since these benefits are accompanied by a host of objective signs in systems (cell energy production function, for example) which are the same in humans and animals, and all involving biochemical pathways which are similar, or identical, it seems that we can indeed take seriously the evidence which these studies have produced.
This then is some of the evidence of what happens to animals and humans when dietary restriction is applied, voluntarily or experimentally, and why we can apply much of this knowledge to our own use. But, what is actually happening to the ageing process itself as these changes occur? How does dietary restriction work?