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Dec. 4, 2006 -- Calorie restriction might help the body's immune system, researchers report.
The findings are based on lab tests on monkeys, not people.
But the researchers note that other studies have linked calorie restriction and longer life in short-lived organisms including worms, flies, and spiders.
The final verdict isn't in yet on calorie restriction and human longevity.
The study was done by Janko Nikolich-Zugich, MD, PhD, of Oregon Health & Science University, and colleagues.
Nikolich-Zugich's group studied 42 monkeys ranging in age from 19 to 23. That's roughly the same as 60 to 70 in humans, the researchers note.
Fourteen of the monkeys had been on calorie-restricted diets for at least a decade. The study doesn't say exactly how much their calories had been cut, or what they weighed.
For comparison, the other monkeys had followed a normal diet their entire lives.
The researchers took blood samples from the monkeys four times over about four years, waiting at least six months between blood tests.
The scientists focused on T-cells, which are part of the body's immune system.
The blood tests showed the T-cells of the calorie-restricted monkeys were less affected by age than those of the monkeys on a normal diet.
The exact reason for the pattern isn't clear.
The study can't show whether the calorie-restricted monkeys will live longer -- or whether the findings will apply to people.But if calorie restriction aids the immune system's T-cells, that might lead to better resistance to infection and, ultimately, to longer life, the researchers note.
SOURCES: Messaoudi, I. Proceedings of the National Academy of Sciences of the United States of America, week of Dec. 4-8, 2006; early edition. WebMD Medical News: "Cut Calories, Boost Longevity?" News release, Oregon Health & Science University. News release, Proceedings of the National Academy of Sciences.