A new study brings scientists closer to an elusive goal: figuring out how to outsmart humans’ biological clocks to slow the aging process and keep people healthier, longer.
For decades, researchers have studied calorie restriction as a potential method of extending lifespan. Numerous promising trials, some dating back almost a century, have been conducted in animals—but the new study, published Feb. 9 in Nature Aging, is significant because it demonstrates that calorie restriction may also slow aging in humans.
A group of researchers, led by scientists from the Columbia University Mailman School of Public Health, used data from a trial called Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE), which tracked a group of more than 200 healthy adults ages 21 to 50 who did not have obesity. Some of the participants were directed to reduce their calorie intakes by 25% for two years, while the rest of the group stuck to their normal diets. Previous research on CALERIE trial participants found that those who ate less over those two years had signs of better health, including improved markers of cholesterol, blood pressure, and blood sugar, compared to those who ate regularly.
For the new study, the researchers wanted to see if people who restricted calories also aged more slowly than those who ate normally. To find out, they used blood samples taken when the study started, at the one-year mark, and at the two-year mark to look for signs of aging in participants’ DNA.
They used three different methods of analyzing DNA. Two of the methods calculated participants’ biological ages, regardless of how old they were chronologically, based on the state of their DNA. Using those methods, the researchers didn’t observe any significant changes after two years of calorie restriction.
The third model was meant to find the rate at which someone is aging, rather than their current biological age. Under that framework, the researchers found that two years of calorie restriction led to a 2% to 3% slower pace of aging. That may not sound like much, but, according to the study’s authors, previous research suggests a similar slow-down in biological aging could reduce someone’s risk of death by up to 15%—roughly the same longevity benefit associated with quitting a smoking habit.
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That’s only an estimate, though. Since people in the study were only tracked for two years, it’s impossible to say exactly how their diets affected their longevity and life-long health.
Plus, a 25% drop in calorie consumption is dramatic and, for many people, unsustainable. Even many of the CALERIE trial participants—who were given a month’s worth of prepared meals to get used to their new eating styles, as well as behavioral counseling—didn’t stick with the plan for a full two years. Those who were able to reduce their daily calories by at least 10% still saw some aging benefit, the researchers found, but not as much as those who ate even less.
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 non-human 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).
Widespread calorie restriction is “not a practical strategy for slowing aging in the population,” the authors of the new study write. But the new data “suggest that slowing aging in humans is possible and provide benchmarks for effects of more scalable interventions, including intermittent fasting and drug therapies.”
Even if they don’t translate into practical advice yet, the study’s findings are a step forward in the effort to understand—and perhaps someday slow, or even reverse—the negative effects of human aging.
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