When it comes to the number of calories we take in, consuming less could mean living longer. Scientists have already found this formula to be true based on laboratory studies of flies, worms and mice. But now there's human proof: Yale University researchers have shown how cutting calories can help keep us healthier by bolstering our thymus gland and boosting our immune system.

More than 200 people participated in the study. First, researchers established each participant’s baseline calorie intake. During the next two years, some participants were told to cut their calories by 14 percent, while the others consumed their usual amount.

Seventy percent of our thymus is over-the-hill, fatty and basically non-functional by the time most of us are middle-aged. The thymuses of those who reduced their calories functioned better.

The research focused on the health of participants’ thymus glands. That’s a gland that makes T-cells, a type of white blood cell that’s a crucial part of our disease-fighting immune system. The thymus is located in our chest, between our lungs. But here’s the Catch 22: our thymus ages fast. By the time we’re around 40 years old, 70 percent of our thymus is already over-the-hill, fatty and basically non-functional.

“As we get older, we begin to feel the absence of new T-cells because the ones we have left aren’t as great at fighting new pathogens,” Vishwa Deep Dixit, a professor at the Yale School of Medicine and the senior author of the study, said in a press statement. To discover if there was any difference in the thymus glands of calorie-restricting participants compared to the others, Dixit and his team used magnetic resonance imaging (MRI) to examine their thymus glands.

They found that the thymus of participants who limited their calories had less fat and greater functionality, unlike people who didn’t reduce their calories. In fact, the thymus gland of those who cut calories was continuing to produce more immune-boosting T-cells. And that’s a big deal. “The fact that this organ can be rejuvenated, is in my view, stunning because there is very little evidence of that happening in humans,” said Dixit. “That this is even possible is very exciting.”

A second part of the study looked at a gene, PLA2G7, in mice to see if reducing it yielded similar benefits as calorie restrictions in humans. The results were positive. The thymus glands of the mice were not only functional for longer, they were protected from eating-related weight gain, as well as age-related inflammation.

How does that help humans? “Identifying these drivers helps us understand how the metabolic system and the immune system talk to each other, which can point us to potential target that can improve immune function, reduce inflammation and potentially enhance life span,” Dixit said. Eventually, with this science in hand, it might be possible to manipulate PLA2G7 and get the benefits of calorie restriction without actually having to restrict calories.

Meanwhile, the NIH’s National Heart, Lung and Blood Institute suggests these simple ways to reduce calories in our daily diets:

  • Limit the amount of meat you eat and substitute veggies, fruits, whole grains and legumes like black beans, cannellini beans and garbanzo beans.
  • Choose water or seltzer water instead of drinking sugar-sweetened juices and sodas.
  • Opt for low-fat frozen yogurt over regular ice-cream.
  • Instead of processed dry cereals eat plain oatmeal with fresh fruit for breakfast.

The study is published in Science.