The key to living longer could be eating less.
In a new study published in the journal Nature Aging, researchers found that a calorie-restricted diet had substantial health benefits, including delayed aging.
"The main take-home of our study is that it is possible to slow the pace of biological aging and that it may be possible to achieve that slowing through modification of lifestyle and behavior," senior study author Dr. Dan Belsky, an assistant professor of epidemiology at Columbia University's Mailman School of Public Health in New York City, told NBC News.
The phase 2 clinical trial included 220 adults who either made a 25% calorie cut to their diet or no changes at all. The body mass index (BMI) for participants ranged from 22 to 27 (a BMI of 30 is the threshold for obesity).
In the first month, those in the calorie-restricted group were given three prepared meals each day so they would be familiar with portion sizes. They were counseled about their diet for the first 24 weeks of the two-year study.
The other group had no counseling or restrictions.
Despite the plan to cut about 500 calories in a 2,000-calorie daily diet, most cut only half that, said Dr. Evan Hadley, director of the geriatrics and clinical gerontology division at the National Institute of Aging (NIA), which funded the study.
"But that 12% was enough to have significant changes," Hadley told NBC News.
Researchers used an algorithm based on past data for 1,000 people who were followed for 20 years, to see how certain DNA biomarkers changed in the study group.
The algorithm was like a "speedometer," Belsky explained, to help gauge the pace at which participants aged.
Those who cut their calories slowed their aging by 2% to 3%, reducing the likelihood of dying early by 10% to 15%.
"We all have the power to change the trajectories of aging," Belsky contends.
Researchers plan to follow those on the calorie-restricted diet for 10 years.
It's not clear why eating less would slow aging, though it may prompt cellular changes, Belsky said.
"It may induce sort of mechanisms of survival responses in the body that have the effect of cleaning up intracellular garbage," Belsky explained. "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.'"
Still, long-term limits on calories have been shown in animals to be harmful, including reduced muscle strength, slower metabolism and an impaired immune system, Valter Longo, director of the Longevity Institute at the University of Southern California, told NBC News. Longo was not involved in this study.
"It may cause powerful anti-aging effects, but also probably some degree of frailty or other issues that may not be so beneficial," Longo said.
People should not starve themselves, Pankaj Kapahi, a researcher at the Buck Institute for Research on Aging, told NBC News. He was not involved in the study.
Kapahi noted that exercise and balanced eating are important for aging.
"Calorie restriction has to be done at a marginal level," he said.