The study, which was funded by the National Institute on Aging, part of the National Institutes of Health, is the first-ever randomized controlled trial that looked at the long-term impact of calorie restriction.
It adds to an already large body of evidence that a calorie-restricted diet can provide substantial health benefits, including delayed aging, said the study’s senior author, Dan Belsky, who is assistant professor of epidemiology at Columbia University’s Mailman School of Public Health in New York City.
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In a phase 2 clinical trial, which ran for two years, 220 adults were randomized to cut their caloric intake by as much as 25% — 500 calories for people who generally consume 2,000 calories a day — or to make no changes to their diet. The participants had a body mass index, or BMI, ranging from 22 to 27.
People in the calorie-restricted group were given three prepared meals each day for the first month to familiarize themselves with portion sizes. They were also provided behavioral counseling about diet over the first 24 weeks. The participants who weren’t in the calorie-restricted group weren’t told how much they should eat and did not get any counseling.
Dr. Evan Hadley, director of the geriatrics and clinical gerontology division at the National Institute of Aging, said that most people in the calorie-restriction group only ended up cutting their daily caloric intake by about 12%.
“But that 12% was enough to have significant changes,” he said.
To measure the rate of aging, the researchers used an algorithm to see how certain DNA biomarkers in the blood changed over time.
The algorithm was based on previously acquired data from about 1,000 people who were followed for 20 years to see how rapidly their organ functioning — including the heart, liver, kidney and lungs — declined as they grew older, Belsky said. The algorithm, he added, acted as a sort of “speedometer,” helping to gauge how quickly participants in the study were aging.
The researchers found that people who cut their calories slowed the pace of their aging by 2% to 3%, compared to people who were on a normal diet.
That translates, Belsky said, to a 10% to 15% reduction in the likelihood of dying early.
“We all have the power to change the trajectories of aging,” he said.
It’s not yet known whether the slowdown in aging would hold out after two years, Hadley said. Participants in the study were not followed up with after the two-year intervention. A separate study, also funded by the agency, is planning to look at the effects of a calorie-restricted diet after 10 years, he added.
Researchers still don’t know exactly why cutting calories appears to slow the aging process, though there is evidence that calorie restriction prompts changes at the cellular level, Belsky said.
“It may induce sort of mechanisms of survival responses in the body that have the effect of cleaning up intracellular garbage,” he said. “It’s a signal to the body, saying, ‘Hey, pay attention. There are resource stresses in the environment. We need to make sure that we are using all of the resources available to us most efficiently.’”
Pankaj Kapahi, a researcher at the Buck Institute for Research on Aging, said that along with calorie restriction, exercise and eating a balanced diet are also important factors to consider for aging. He was not involved in the research.
“You need multiple interventions to see the full effects of health,” he said.
Kapahi added that the study’s findings do not mean people should starve themselves, saying that could lead to malnutrition and poor mental health.
“Calorie restriction has to be done at a marginal level,” he said.
Valter Longo, a biochemist and director of the Longevity Institute at the University of Southern California, said that limiting calories for extended periods of time can be harmful.
Studies in animals, for example, have shown that long-term calorie restriction was found to be associated with a risk of reduced muscle strength, slower metabolism and an impaired immune system, said Longo, who was not involved in the study.
“It may cause powerful anti-aging effects, but also probably some degree of frailty or other issues that may not be so beneficial,” he said.
Hadley cautioned against over-interpreting the results, saying calorie restriction may not be for everyone, including those with multiple underlying conditions. He advised speaking with a doctor before undergoing a calorie-restricted diet.
“It’s not like this is somehow this universal key to aging and so it’s going to slow everything down,” he said.
Source: Berkeley Lovelace Jr, NBC HEALTH
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