Calorie restriction is often thought of as a short-term measure to lose weight, but data from the Pennington Biomedical Research Center shows there are major benefits when practiced long-term. Study participants who completed a two-year calorie restriction program saw unexpected improvements in immune function that are associated with longevity.
The study found people who reduced their normal calorie intake by 14 percent daily during the trial period generated more T cells, which play a vital role in immune function and are also helpful in slowing the aging process. These results not only point to longer years alive, but also more years in good health.
"Two years of modest calorie restriction reprogrammed the pathways in fat cells that help regulate the way mitochondria generate energy, the body's anti-inflammatory responses, and potentially longevity," said Eric Ravussin, Ph.D., Associate Executive Director for Clinical Science at Pennington Biomedical Research Center. "In other words, calorie restriction rewires many of the metabolic and immune responses that boost lifespan and health span."
The study results were published in a recent edition of the journal Science. They were derived from Pennington Biomedical’s CALERIE study (Comprehensive Assessment of the Long-Term Effects of Reducing Intake of Energy). It’s the longest-running calorie-restriction study ever conducted with humans.
At the center of the study was a focus on the thymus, a gland that is located above the heart. It is vital to the immune system and the location where T cells, a type of white blood cell, are produced. Research shows the thymus ages at a rate faster than most other organs.
It is estimated by the time a person reaches the age of 40 the thymus is roughly 70 percent fatty and non-functional. The decreased ability to generate T cells is one reason elderly people are at greater risk of illness.
"As people age, their thymuses shrink and produce fewer T cells," Ravussin said. "As a result, older people have a harder time fighting off infections and certain cancers. Calorie restriction helps prevent the thymus from shrinking so the person generates more T cells."
Researchers used magnetic resonance imaging (MRI) to assess the thymus and found a big difference between those who restricted their caloric intake and those who didn’t. The thymus of those in the calorie-restriction group had less fat and greater functional volume than they did at the start of the study. That means they were producing more T cells than they were two years prior.
The group that did not restrict their calories had no change in the functional volume of their thymus.
Dr. Ravussin said the increase in T cells is also associated with an improved ability to burn stores of fatty acids for energy. That’s important because fat that is not burned will likely build up in the body leading to obesity, insulin resistance and type 2 diabetes.