Penguin power
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.