Flex Those Nerves
May Your Days Be Long and Stressful
By GINA KOLATA
Published: September 21, 2003
To many, the good life may be lying on a hammock strung between palm trees, sipping a long cool drink, doing nothing, planning nothing, worrying about nothing.
But the latest scientific research offers more evidence that this version of the the good life and good health may not be the same thing.
Of course, the research is preliminary and involves mostly insects and rodents, but some experts, like Dr. Mark Mattson, chief of the laboratory of neurosciences at the National Institute on Aging in Baltimore, are taking no chances.
He has been on a low-calorie diet for 20 years, starting when he was a 26-year-old graduate student. He skips breakfast and eats a meager lunch, concentrating the semi-starvation effects into one discrete period. Then he consumes a more normal dinner. He is 5-foot-9 and weighs 120 pounds. He also exercises each morning.
His goal is to subject his body to daily low-level stress — like abstaining from food for much of the day. "Stress is a very ill-defined term, and there's clearly bad types of stress," Dr. Mattson said. "It is very clear that uncontrollable chronic stress and psychological stress is bad for the brain and the body." But, he and others say, mild stress is a very different, beneficial thing.
These conclusions are emerging from animal studies that probe why low-calorie diets prolong life. One early idea was that the diets reduce the lifelong wear and tear on the body, which contributes to aging, so that if you are on a restrictive diet for your whole life, or most of it, you will live longer.
But scientists in London reported last week that the protective effect of low-calorie diets in fruit flies pops up within 48 hours after the diet begins. It goes away just as quickly, so that a fly that starts dieting in middle age is in the same shape as one that had been dieting all along. One that dieted until middle age and then stopped is the same as one that had never dieted at all. In every case, something seems to be happening overnight to allow the insects to resist diseases or injuries that would have killed them.
Low-calorie diets, in animals at least, increase resistance to dying from infections or from the stress of extreme temperatures. Such diets also prompt the release of things like antioxidants and proteins that protect cells, said Dr. Huber Warner, director of the biology of aging program at the National Institute on Aging. Even the discovery, announced last month that a chemical in red wine, resveratrol, mimics the response to starvation in yeast and fruit flies, is part of the stress story — it activates a protein, sirtuin, made in response to stress.
You may not even have to diet every day, Dr. Mattson says. He put mice on a program in which they starved one day and ate their fill the next. The animals did not lose any weight, but they lived 30 percent longer than mice that ate every day and the same as mice placed on a constant diet. The intermittent diet also elicited the same mild stress response as a constant diet.
That response included more nerve growth factor in their brains, a substance that prompts nerve cells to grow, survive and be more resistant to disease. In addition, when intermittently dieting mice ate, their blood sugar levels were better than those of animals that were not dieting, what Dr. Mattson calls "a sort of anti-diabetic effect." And when he placed them under stress by immobilizing them with tiny straitjackets or making them swim in cold water, the dieting mice recovered much faster than the others.
Scientists say exercise, too, may prolong life by providing low-level stress. In studies, rodents live longer on average with regular exercise, largely because they are less prone to cancer. That regular physical exercise also increases the levels of nerve growth factor in animals' brains, in much the same way as intermittent fasting does.
Study after study has observed that people who engage in moderate exercise most days of the week (say, a brisk walk) live longer, but it is not clear why. They do not exercise enough to lose weight, nor enough to make much difference in their blood pressure or their cholesterol levels.
Astonishingly, there is some evidence that even the stress of low-level radiation seems to make cells hardier, Dr. Warner said, not that he or anyone else is advocating that you subject yourself to X-rays for your health.
"I think this is not unreasonable, that the body evolved a general mechanism to respond to stress," Dr. Warner said. Low-calorie diets, he added, might be just one way to elicit it.
And the stress-free life, Dr. Mattson added, might be the worst way to live. "If you are a couch potato, getting no physical exercise and no mental exertion, your cells become complacent. They are not stressed so why should they do anything?"