“Just because you haven’t lost weight doesn’t mean you’re not reaping the benefits of exercise in some way,” says exercise physiologist Samantha Heller, M.S., R.D.N., adjunct professor of nutrition and health at the University of Bridgeport, and senior clinical nutritionist at NYU Langone Health. “There’s no downside to getting out the door and exercising on a regular basis,” she tells SELF.Health benefits aside, running can be just plain fun. After all, any runner can attest to the feelings of freedom and excitement you experience when you really hit your stride. So try not to let the discussion of whether or not running is “good” or “bad” for your weight slow you down. Now, let’s dig into some more science.Here’s why some people may lose weight from running. This can happen in a few different ways, but they each largely come down to calorie intake vs. expenditure as Rachel Pojednic, Ph.D., assistant professor and director of exercise science at Norwich University in Vermont, and former research fellow at the Institute of Lifestyle Medicine at Harvard Medical School, tells SELF. (Remember, that’s not the whole story when it comes to weight, but it’s a big part of it.)If taking up running increases a person’s overall physical activity, and they don’t make any other changes to the way they eat, then they may start to lose weight from now expending more calories than they’re taking in. It’s also possible to lose weight from the combination of running and other simultaneous changes. “Oftentimes what you see is that people are combining some kind of positive health behaviors around [running],” Dr. Pojednic says. For instance, someone who has fallen in love with a running practice may start sleeping more, drinking less alcohol and more water, and loading up on nutrient-rich foods to have enough energy for chasing those endorphins. All of these factors can combine in a way that causes weight loss, at least while these behaviors are maintained. Most of this weight loss will come from adipose tissue (otherwise known as body fat), but some of it may also come from lean mass (otherwise known as muscle tissue). One way to hang on to this muscle mass during any new workout plan is to make sure you’re getting enough protein, “so your body has the building blocks to rebuild that muscle tissue that you are naturally breaking down from exercising,” Dr. Pojednic says. Another strategy is to add some resistance training to your workout plan too, which is a great way to maintain or add muscle. Here’s why some people may gain or maintain weight from running. Similar to the above, a lot of this comes down to calorie intake vs. expenditure. A 2019 study published in The American Journal of Clinical Nutrition found that people often increase their calorie intake when they exercise. It’s certainly not uncommon to start a running plan and realize that you’re suddenly way more famished than usual. And, what’s more, there’s absolutely nothing wrong with that, even though weight gain tends to be demonized. Bodies need fuel, especially for increased exercise!