Caloric restricted (CR) diets are lower in calories but not essential nutrients. CR diets can bring on changes in the molecular processes associated with aging, such as DNA methylation, that lessen aging's effects. Studies have found calorie restriction can increase the lifespan of multiple species, including worms, flies and mice.

A new study by a team led by researchers at Tufts University looked at the relationship between calorie restriction and DNA methylation data in humans. Participants in the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy (CALERIE) trial were randomly assigned to either a 25 percent calorie-restricted diet or a control group that continued eating their usual diet during the two-year study period.

Calorie restriction slowed the pace of aging by two to three percent, which other studies have found translates to a 10 to 15 percent reduction in mortality risk. This effect is similar to that of a smoking cessation intervention.

The third measure of the data estimated the rate of biological deterioration over time. It can be thought of as a “speedometer” that displays how fast a person is aging.

The fact that following a CR diet for a relatively short time period had an effect on the pace of aging “is particularly important because it provides proof of concept that we can move the needle on the pace of aging in a very controlled context,” Calen Ryan, a co-author on the study, told TheDoctor. Ryan pointed out that though a CR diet is not for everyone, the findings give researchers an idea of what effects they might see in trials of other types of calorie-restricted eating, such as intermittent fasting or time-restricted eating.

Participants in the intervention group were able to achieve a reduction of about 12 percent of their daily calories reduction on average. “Even with this modest reduction in caloric intake, they still got the benefits of the CR diet, which was exciting,” Sai Krupa Das, a co-author on the study, added.

Of the 220 CALERIE participants, 145 were randomized to the calorie restricted diet and 75 were randomized to the control group. Blood samples were collected from participants at enrollment, after 12 months and again after two years. Methylation marks on DNA extracted from the white blood cells were analyzed. These chemical markers adhere to the sequence of DNA that regulates gene expression and change with aging.

The main analysis looked at three measurements of the DNA methylation data, also called epigenetic clocks. The first two estimated participants’ biological age, regardless of their actual chronological age. These measures can be thought of as “odometers” that provide a static measure of how much a person has aged, explained Ryan, a research scientist at the Columbia University Mailman School of Public Health.

The third measure of the data estimated the rate of biological deterioration over time. It can be thought of as a “speedometer” — it displays how fast a person is aging.

The calorie restricted diet slowed the rate of aging, but it had no significant effect on participants’ biological age.

Das, a scientist at the Human Nutrition Research Center on Aging at Tufts, is currently leading a follow-up study investigating what, if any, long-term effects calorie restriction has on healthy aging. “Our follow-up study will test if the short-term effects of the CALERIE intervention translate into a longer-term reduction in age-related chronic diseases or their risk factors,” she said.

The study is published in Nature Aging.