Megan Markoff , director of nutrition at coaching company Pallas , was scrolling Instagram when she saw a controversial post claiming “running made me fat.” She grabbed her phone and recorded a response video that later went viral, rebutting the statement. “I see this all the time. What usually happens is a mismatch between training and nutrition,” Markoff said to the camera .

Across social media, influencers are increasingly warning that long-distance running leads to weight gain. “I didn’t even understand how prominently this narrative was getting pushed on social media until a new client told me about it,” Markoff tells Runner’s World.

But the reality is nuanced.…