There are the runners who swear by eating something to get them through a morning run, while others can't stomach the thought of going on a six-miler after a meal, no matter how small it is. But is one way better than the other?
Some believe that exercising without eating beforehand causes your body to better burn fat. For example, trainer Yumi Lee, who's trained Jessica Alba , recommends not eating anything if your workout is within an hour of waking up in order to boost metabolism . Others, however, point to studies that show that exercising on empty can lower your body's calorie-burning potential by holding onto fat and burning muscle instead .
The answer to whether you should eat before your run, then, may purely depend on preference. Several other studies have found little to no difference between running before or after breakfast — one study found, for example, that while eating before an hour-long run helped control appetite later on in the day, exercising without eating  also did almost as well. Another study found that while eating breakfast before a moderately intense run helped runners consume fewer calories  later in the day, it also reversed the effect of the post-workout appetite-suppressing hormones. And while eating a carb-and-protein-filled snack before a run can boost your endurance to help you burn more calories in the long run, dealing with gastrointestinal issues from your morning meal can cut your calorie-burning workout short.
Whatever your preference, another small study may point to a benefit of eating before you head out the door. In it, the researchers found that runners who had fasted before their workout had increased mental fatigue and reported being in a worse mood  than when they ran after eating breakfast. Not only that, their bad moods lasted well after they finished their workout. If you don't want to start the day on the wrong foot, at least a small pre-workout snack  may be just what you need.