UPDATE: Several studies have shown that animals fed a nutritionally balanced diet - but given only 50 percent to 60 percent of their normal caloric intake - tend to live much longer than controls that eat normal amounts of food. The first of these experiments (using rats) was reported in 1935, with the rats showing up to a 50 percent increase in life span. These findings have been confirmed not only in rats, but in mice, hamsters and such non-mammals as fruit flies and fish. Not only is the life span extended, but physiologic signs of aging and the diseases of old age were delayed or prevented.
The question might be asked, "Would it be good for all of us to decrease our caloric intake in order to live a longer life? This question was discussed in the October 1990 issue of the University of California, Berkeley, Wellness Letter.The major problem, according to this article, is determining whether the methods that lengthen the lives of rats, mice or other small animals would lengthen the life of humans. Studies using rhesus monkeys are now being done at the Francis Scott Key Medical Center in Baltimore under the auspices of the National Institute on Aging. However, it may be some time before results emerge from this study because monkeys live much longer than rats and other small animals. And, even if the monkeys live longer, there would still need to be evidence that these techniques would help humans.
One researcher, Dr. Roy Walford of UCLA Medical School, was quoted as saying that caloric restriction would decrease the rate of aging in humans. However, in animals, this decrease in calories leads to a fairly miserable life. The activity level in these animals is reduced dramatically, and the resistance to infectious diseases is so low that they must be protected from exposure to infections or they die early from other causes. In human starvation studies, the ability to work is seriously impaired, and the outcome is often malnutrition and disease - not longer life.
Why does eating less increase the life span of these small animals? No one really knows, but the theory is that the decrease in calories somehow shifts the body's focus away from reproduction and growth to maintenance and repair. If this is really the cause of longer life, it would be difficult to understand how lower intakes could help a 55- or 60-year-old human who would have already "shifted focus" from reproduction and growth to maintenance and repair.
The recommendations of the Berkeley Newsletter staff is that a person would be ill-advised to cut calories dramatically in an attempt to live a longer life. They point out that the diet of rats and monkeys in the laboratory is carefully monitored so that the animals get adequate vitamins, minerals and other nutrients. In addition, these animals are not concerned about the quality of life and are protected from the harsh environment of the real world.
Even decreasing calories for weight control can cause problems and most weight control experts (including me) prefer only a moderate decrease in calories with the major change occurring in the type of food the person eats.