There's no getting around the fact that aging leads to a gradual breakdown of our bodily systems—and, in turn, causes a host of annoying ailments like creaking joints, reduced lean muscle, and higher risk of chronic disease. One particularly irksome aspect of old age is the inevitable accumulation of fat around your waistline. You can keep it a bay for a long time with a healthy diet and lots of exercise, but eventually it will start to pooch out.

Now, we have another cause to blame: As some immune cells (called macrophages) age, they get inflamed and prevent fat-burning neurotransmitters from firing properly, according to new research from Yale that was published in the journal Nature.

In the experiment, scientists pulled the immune cells from young and old mice, and studied their genes. They discovered that the older macrophages destroy the nerve cells that allow fat cells to offer themselves as fuel when the need comes. The result? More belly fat.

"The key finding is that the immune cells talk to the nervous system to control metabolism," said study lead Vishwa Deep Dixit, Ph.D., a professor of comparative medicine and immunobiology at Yale. The researchers also stated that if controlling inflammation in aging immune cells can improve metabolism, it may have other positive effects on the nervous system or on the process of aging. "The purpose of our research is to achieve greater understanding of immune cell interactions with nerves and fat cells to potentially reduce belly fat, enhance metabolism, and improve performance in the elderly," said study co-author Christina D. Camell, Ph.D.

For now, though, we recommend hitting the gym and mixing weight lifting with cardio—for the rest of your life—if you want to keep belly fat at bay as long as possible. Oh, and stay away from empty calories and junk food, too. Here are some healthy recipes to get you on the right track.