You don’t need it, but new research published in the journal Cell found another reason to exercise: It reduces risk for stress-induced depression.

This kind of depression joins the existing benefits of exercise, including reducing risk for other illness while also promoting weight loss, mental health, bone density, and blood circulation. Let’s not forget the food, the endorphins, and did we mention the food? Researchers from the Karolinska Institutet in Sweden chose to focus on depression since this particular association isn’t exactly refined.

"In neurobiological terms, we actually still don't know what depression is,” Mia Lindskog, researcher at the Department of Neuroscience at Karolinska Institutet, said in a press release. “Our study represents another piece in the puzzle, since we provide an explanation for the protective biochemical changes induced by physical exercise that prevent the brain from being damaged during stress.”

Lindskog and her team used mice to explain these changes: one group of normal mice and a group of genetically modified (GM) mice. The GM mice had high levels of the muscle-conditioning protein PGC-1-alpha-1, and for five weeks researchers exposed both groups of mice to a stressful environment. Think loud noises, flashing lights, as well as reversed circadian rhythm at irregular intervals.

Following this stressful time, the normal mice developed depressive behavior while the GM mice did not. "Our initial research hypothesis was that trained muscle would produce a substance with beneficial effects on the brain,” said Jorge Ruas, principal investigator at the Department of Physiology and Pharmacology at Karolinska Institutet. “We actually found the opposite: well-trained muscle produces an enzyme that purges the body of harmful substances. So in this context the muscle's function is reminiscent of that of the kidney or the liver.”

The enzyme is called KAT, which Ruas explained works to “convert a substance formed during stress (kynurenine) into kynurenic acid, a substance that is not able to pass from the blood to the brain.” It isn’t scientifically found, but high levels of kynurenine can be measured in patients with mental illness. For the normal mice in the study, when they were subjected to it, they continued to exhibit depressive behavior in comparison to non-depressed GM mice.

Basically, all you exercise naysayers: It’s time to eat crow. Even if you’re discourasged by this study’s mice subjects, separate, human research from the University of Toronto found moderate exercise can prevent episodes of depression. Another study review done by Harvard Health Publications found regular exercise can improve mood in people with mild to moderate depression.

We'll see you guys out there.

Source: Agudelo L, Femenía T, Orhan F, Porsmyr-Palmertz M, Goiny M, et al. Skeletal Muscle PGC-1a1 Modulates Kynurenine Metabolism and Mediates Resilience to Stress-Induced Depression. Cell. 2014.