The most dramatic lifespan extension seen to date in warm-blood mammals is food restriction, which has prolonged survival in dozens of studies in both rats and mice, starting with the pioneering studies of Cornell University nutritionist Clive M. McCay in the 1930s.
When started very early in life (just after weaning), severe food restriction has delayed physical and sexual maturation, and led to very large increases in maximum lifespan. The longest-lived, food-restricted animal to date was studied by Morris Ross of the Institute For Cancer Research in Philadelphia. This rat lived for 1,830 days, which is more than 5 years, and well beyond the world record for rat survival under natural conditions.
In the 1980s, Richard Weindruch and Roy Walford (of UCLA Medical Center) showed that the lifespan of middle-aged mice could be extended (moderately) by depriving them of food (with nutrient supplementation) gradually over an extended period of time.
Food restriction is accepted by virtually all gerontologists as a regimen that definitely extends maximum lifespan in rodents (and possibly in humans). Studies have shown that food restricted animals show many signs of retarded aging including delayed deterioration in connective tissues, hormone output, visual capacity, strength, coordination, and energy production. (Studies are currently underway to determine the effects of food restriction in monkeys).
However, the physiological mechanisms of action by which food restriction retards the aging process are not known, although there have been several credible hypotheses to explain it including reduced free radical activity and enhanced neuroendocrine stabilization.
The Pineal Gland In Food-Restricted Rats
In the late 1980s, a research team, including scientists from the University of Texas at San Antonio working with scientists from Norway and Germany, studied the effects of food restriction on the pineal gland in very old male Fisher 344 rats (28 months old), roughly equivalent to 80 years of age in humans, and in young, normally-fed rats (3 months of age).
In this study, the experimental rats were divided into two groups when they were six weeks of age, with one group receiving 60% of the calories consumed freely (ad libitum) by the rats before the experiment was started. They were then individually caged and maintained until 28 months of age, when 5 old food restricted rats and 5 old normally-fed rats were sacrificed, examined, and compared with 11 young rats.
Results Of Study
There were many striking differences between the old food-restricted and normally-fed rats. The normally-fed rats weighed 29% more than the food-restricted rats. They had overt pathological lesions--three with tumors and two with cataracts in both their eyes. Apart from one rat with a cataract, the food-restricted animals all appeared to be in good health.
How Pineal function Was Affected
The old food-restricted rats displayed significantly higher pineal and serum (blood) concentrations of melatonin (as well as higher levels of the enzymes involved in melatonin synthesis), although the melatonin levels were not as high in the old, food-restricted rats as in the young rats.
The condition of the pineal glands in the old, food-restricted rats was much better than in the old, normally-fed animals. They showed less cell loss, better structure, and more youthful function than the pineal glands in the normally-fed old animals, which were calcified and decrepit in comparison.
Does Food Restriction Work Through Pineal Action?
The scientists suggested that the anti-aging, life span extending effects of food restriction in laboratory animals may occur because of the preservation of youthful pineal function. As they put it:
"Based on a positive correlation between the present findings of elevated pineal activity in old, food-restricted rats and a retardation of age-related physiological deteriorations, absence of pathological manifestations and longevity in such animals, we propose that the pineal gland, through its secretion of melatonin, may be regarded as a possible neuroendocrine mediator between food restriction and some of the age-related changes. The present findings are similar to those in mice which were treated with melatonin."
Melatonin and Body Temperature