You hit the fast food drive-through a couple times a week, and your grocery cart is regularly filled with cookies, packaged doughnuts, ice cream, chips (and dip). But you’re thin. You run—a lot—and you’re not gaining any weight, so all’s good, right? Well, not exactly. Put down the chocolate cupcake and hear us out. While runners do tend to be much healthier than the general population, with lower rates of diabetes and heart disease, that’s largely due to a healthy diet rather than running regularly, says Sara Mahoney, Ph.D., chair of the department of exercise science at Bellarmine University. In...