Yes, staying active is absolutely essential to a healthy lifestyle—the American Heart Association recommends at least 150 minutes of moderate exercise per week. But if your aim is weight loss specifically, and you find yourself hitting a plateau despite clocking in some serious gym time, the culprit is likely your diet. In fact, according to new data, what you eat is far more important than how active you are when you’re trying to slim down.

Curious about her thoughts on the matter, I reached out to New York City nutritionist Dana James, MS, CNS, CDN, who confirms Carroll’s point. “I always tell my clients that it’s 80 percent diet, 20 percent exercise,” she says. “It’s definitely most important to get the diet right, especially since we tend to underestimate what we eat and overestimate what we burn.” Moreover, the more we lose weight, the lower our calorie burn (a 200 pound woman will burn far more calories in spin class than a 120 pound woman).

Carroll also points out that exercise tends to make us eat more, but James notes that you can still counteract this the right way. “It’s not about eating less, but eating right,” she says. In other words, if you trade your post-run Chipotle burrito for an equally filling but healthy meal, then you’ll be that much more likely to see the scale dial go down.

That isn’t to say that exercise isn’t important—20 percent is still significant, and beyond factoring into weight loss, the benefits of staying fit range from battling diseases to promoting a longer, healthier life. Plus, building more muscle encourages a higher, more sustained metabolism, even at rest.

So by all means, continue to pound the pavement, hop on your SoulCycle bike, and/or frequent your favorite barre class—just be sure that if slimming down is your goal, you’re filling up on the healthy stuff. (Sorry, cheesy, guac-filled, wonderful burritos.)