It works with worms, rats, mice and monkeys. Reduce an animal’s intake of calories by 30% and it will live 30% longer than those on an ordinary diet.
Now scientists want to know if the same severely restricted diet that has produced dramatic results in laboratory experiments in animals will work in humans. In September, the National Institute on Aging began scientific trials involving about 200 people at three locations in Louisiana, Massachusetts and Missouri. The volunteers are eating low-calorie diets to see if a significant reduction in calorie consumption will improve their health and enhance the likelihood of a longer life span. The institute’s trials are noteworthy because the latest government figures show that a disturbing 61% of American adults are overweight, increasing their risk of heart attacks, strokes, diabetes and arthritis. Finding a diet that delivers maximum nutrition while sharply reducing calories -- and that people will stick with -- is a key goal of the research project.
Moreover, the public’s appetite for remedies to slow the aging process is voracious. From memory pills to hormone shots and anti-wrinkle creams, the business of anti-aging is booming, but these products often make claims that are unsubstantiated by rigorous science. There is no pill or potion that has been proved to extend the human life span. The only scientifically demonstrated tool for increasing longevity is caloric restriction -- and it remains unproved in humans.
“We cannot guarantee the fountain of youth,” said Dr. Charles Hollingsworth, the institute’s chief of clinical trials in the geriatrics and gerontology program. But the payoff should be better health and the longer life that comes with a stronger immune system.
In the institute studies, some volunteers will try calorie restriction alone, while others will combine fewer calories with an exercise regimen. The scientists want to know if independent, impulsive human beings can get the same results with a highly disciplined diet as do laboratory animals who have no choice in the matter. The results of those on the special diet will be compared to a control group of similar people who are not changing their dining habits.
Because the human life span is so much longer than that of laboratory rodents, researchers won’t know for a generation or more whether the calorie-restricted diet actually helps humans live significantly longer. For now, the scientists hope that the result of the highly disciplined diet will be better health into advanced old age.
“We’re not going to stop heart attacks and strokes, but I would much rather trade for a heart attack at age 85 than age 50,” Hollingsworth said.
Scientists and nutrition experts at Louisiana State University, Tufts University in Massachusetts and Washington University in St. Louis will be trying to get their human subjects to do something millions of Americans have attempted and failed: finding a good diet and sticking to it. This means a volunteer in the study must trim 25% of the usual consumption of calories. Someone who has been consuming a daily diet of, say, 2,000 calories will be asked to cut back to 1,500, without veering off course.
It’s a hard task: The recidivism rate for dieters is more than 90% -- that’s the percentage of people who go on diets but gain all the weight back within five years. Scientists have long known that the miracle cure that works in animals doesn’t always work in humans. It is relatively easy to control the habits and extend the lives of caged lab rats, with food doled out carefully each day by a researcher. It is much harder to imagine controlling the caloric intake of human beings, bombarded as they are by marketers’ images of humongous hamburgers, super-size sodas and fatty desserts.
Researchers in aging say that if calorie restriction worked in human beings as it has in animals, people who now live into their 80s would routinely live until age 110 or beyond. And those extra years would be healthy ones. They would eventually succumb to cancers, strokes and heart attacks just as people do now, but at a more advanced age. As the body goes through normal aging, it must work harder, putting more strain on the various organs and the immune system. When we take in a surplus of calories, the body must cope with processing more nutrients than are really needed. If you can reduce calorie intake, you keep the body in better balance and it needn’t work so hard, said Hollingsworth.
Nobody knows for sure why reducing caloric intake leads to increased longevity. One theory is that it is part of the natural survival mechanism of successful species. When the organism senses less food is available, it slows down to conserve energy. Metabolism goes into low gear, reducing the production of toxic waste materials. A slower rate of activity translates into a longer life span. In simple worms, called nematodes, caloric restriction results in dramatic changes. The worms become immune to heat and chemicals that would otherwise kill worms on a more normal diet. In higher animals, there are different reactions.
The monkeys on caloric restrictions, who have a diet fortified with extra vitamins and nutrients, live a longer and healthier life than their lab mates who get a fuller diet, said Donald K. Ingram, acting chief of the laboratory of experimental gerontology at the institute.
The institute’s studies on humans are looking at various methods of reducing caloric consumption. One approach will be to reduce caloric intake in the diet by 25%; another is a combination of partial caloric reduction and exercise. Different age groups, ranging from 25 to 60, have been enrolled in the studies. The approach that has the best results will then be used in larger trials with thousands of people.
If scientists can figure out how caloric restriction slows down the aging process, perhaps someday they can find a magic pill to increase human longevity. But that’s a dream for another day.
A sample menu
A day’s menu suggestions from “Beyond the 120-Year Diet” by Dr. Roy L. Walford.
1 1/4 cups rolled oats, cooked
1/4 cup wheat bran
1 banana, sliced
1 glass skim milk
3 oz. grilled halibut
1/2 cup cabbage (as cole slaw), with 1 tablespoon low-fat dressing
1 slice whole-wheat bread
1 glass skim milk
Oyster cocktail (4 to 8 oysters, depending on size)
Pasta primavera (from recipe in book)
6-8 leaves kale, steamed, with sauce (from book recipes)
1 slice watermelon, equivalent of 2 cups, or other fruit
Total calories: 1,301
Percentage of calories from protein: 26%
Percentage of calories from fat: 14%
Percentage of calories from carbohydrates: 60%
Total protein: 84 grams
Total fat: 20 grams
Total carbohydrates: 215 grams
Fiber: 33 grams
Cholesterol: 119 grams