Calorie restriction can slow aging in healthy adults, according to new research published in the journal Nature Aging. And while the effects are small on an individual level, the societal impact could be substantial.

In a news release, the international research team led by Columbia University’s Butler Columbia Aging Center said it was a first of its kind randomized controlled study of long-term calorie restriction in healthy, nonobese adults. Researchers found that cutting calories slowed aging at a pace comparable to quitting smoking.

“In worms, flies and mice, calorie restriction can slow biological processes of aging and extend healthy lifespan,” senior study author Daniel Belsky, an associate professor of epidemiology at the center, said in the release. “Our study aimed to test if calorie restriction also slows biological aging in humans.”

Those who restricted calories slowed their pace of aging by 2%-3%, which translated to a 10%-15% reduction in the likelihood of dying early, per the study.

Study mechanics

The CALERIE study — it stands for Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy — is a phase 2 clinical trial funded by the National Institute on Aging. It involved 220 men and women at three different U.S. sites who were randomly assigned either their normal diet or one with a 25% calorie-intake reduction.

As NBC News reported, “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 on Aging, said most participants who were restricting calories only cut their daily intake by about 12%, but it was “enough to have significant changes.”

Biological aging was measured using blood samples collected at the start of the trial and after 12 months and 24 months. In the background material, Belsky said, “Humans live a long time, so it isn’t practical to follow them until we see differences in aging-related disease or survival. Instead, we rely on biomarkers developed to measure the pace and progress of biological aging over the duration of the study.”

In this case, they used chemical tags on the DNA sequence that regulate gene expression and which change with aging. They looked at estimates of biological age “at which a person’s biology would appear ‘normal,’” and also at the pace of aging.

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According to the study, “Treatment effect sizes were small. Nevertheless, modest slowing of the pace of aging can have profound effects on population health.”

Long-term not known

Study co-author Calen Ryan, a research scientist at the aging center, said that while the pace of aging was slowed, “calorie restriction is probably not for everyone. Our findings are important because they provide evidence from a randomized trial that slowing human aging may be possible. They also give us a sense of the kind of effects we might look for in trials of interventions that could appeal to more people, like intermittent fasting or time-restricted eating.”

The researchers are also following up to see the benefits or risks and whether calorie restriction has long-term impact. This study only followed people for a couple of years.

Pankaj Kapahi, a researcher at the Buck Institute for Research on Aging who was not involved with the study, told NBC News that exercise and eating a balanced diet are also important factors for healthy aging.

“You need multiple interventions to see the full effects of health,” he said.

And some caution that long-term calorie restriction can create problems. Valter Longo, a biochemist and director of the Longevity Institute at the University of Southern California who was not part of the study, told NBC News that animal studies suggest that long-term calorie restriction is associated with a risk of weaker muscles, slower metabolism and a less-effective immune system.

A NewScientist analysis says bluntly that the jury’s still out on whether cutting calories long-term is a good idea or even effective.

And Time reported that “some researchers have raised concerns about the potential drawbacks of long-term calorie restriction among people, including mental health consequences and declines in bone density and muscle mass. One 2018 study on nonhuman primates also found that calorie restriction can extend lifespan, but may also change the composition of the brain (albeit not in ways that affected cognitive function, according to that study).”

Other approaches

The calorie-restriction study is not the only Columbia research focused on slowing aging. Earlier this month, researchers said they are looking at “young blood” to see if it can slow the impact of time.

“Young blood has a rejuvenating effect when infused into older bodies, according to recent research: Aging hearts beat stronger, muscles become stronger and thinking becomes sharper,” Columbia said in a news release from its stem cell initiative.

While some scientists are trying to figure out the elements of young blood that could be “captured or replicated and put into a pill,” one question posed at Columbia is “what if the best way to get the benefits of young blood is to simply rejuvenate the system that makes blood?”

Those findings are published in Nature Cell Biology.

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