Sharply cutting calories in the diets of rhesus monkeys was found to reduce aging-related deaths, according to a study that followed 76 monkeys for two decades.
The findings, published Thursday in Science magazine by researchers at the University of Wisconsin, give new impetus to researchers and companies, including GlaxoSmithKline PLC, that are searching for a drug to mimic the beneficial effects of a meager diet in humans without the feeling of near-starvation.
For thousands of people who already attempt to sharply restrict their food intake -- by as much as 30% below a normal diet of roughly 2,200 calories a day -- in an effort to live longer, the findings appear to validate a technique called calorie restriction as a way to live longer.
Scientists have known since the 1930s that the technique lengthens the lives of mice. But until now, no study had shown the technique worked in monkeys, which are more genetically similar to humans. One difficulty: Monkeys live almost 30 years on average, meaning any study to measure a difference in death rates would need to wait a long time.
The Wisconsin study, which began in 1989 with 30 rhesus monkeys and added 46 more in 1994, is the first to yield a definitive finding. Researchers began restricting half the monkeys' diets, reducing their calories by 30%, when the monkeys were fully grown, or about 10 years old.
Thursday's findings are "all consistent with what human practitioners of calorie restriction have always believed," said Brian Delaney, president of the Calorie Restriction Society, which claims about 3,000 members. "Any degree of restriction beyond what you're currently eating will confer health benefits and will slow the aging process," he said.
After almost 20 years, 14 of 38 monkeys in the control group had died of what were considered age-related causes, such as heart disease and cancer. That compares with only five of 38 monkeys in the restricted-diet group, a significant decrease. However, the difference wasn't statistically significant when considering all causes of death, including monkeys who died from injuries and complications from anesthesia.
Calorie restriction also appeared to slow the loss of gray matter in the brain.
"It's a pretty simply story, really," said Richard Weindruch, a Wisconsin professor who led the study. "We've been waiting all these years for the monkeys to become old enough to get meaningful data on lifespan and brain aging and diseases."
Dr. Weindruch described himself as an imperfect adherent to calorie restriction. "I found it difficult to adhere to such a diet, despite studying it for so many years," he said, adding he had been able to cut his calories by about 20% for only a few months. "I'm not the poster child for human application," he said.
He is the co-founder of a Wisconsin company, LifeGen Technologies LLC, that works with drug makers to quantify the effect of possible life-extending drugs.
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