Is it best to eat before your run or to wait until after? The answer is not so simple. As Healthline reported, certain findings suggest fasting before exercise may help burn more fat, but some experts aren’t sure that strategy is good for overall fitness. Here’s what you need to know to decide for yourself:

• A 2017 study published in American Journal of Physiology - Endocrinology and Metabolism found that ten overweight, but otherwise healthy, men used more fat for energy when they fasted before a moderate-intensity walk than when they ate before the walk.
• A meta-analysis published in the British Journal of Nutrition concurred with the 2017 study: after looking at data from 27 studies with a total of 273 participants, researchers found that, compared with eating before exercise, fasting resulted in increased fat usage for energy during exercise.
• Another study also published in the British Journal of Nutrition found that, after an overnight fast, skipping breakfast boosted fat burning. The 12 active men included in the study used 20% more fat for energy during a moderate-intensity run when they skipped breakfast, compared with when they ate breakfast.

While these studies found fasting to be beneficial in terms of fat tissue breakdown, some experts aren’t convinced this is ideal. For example, Jennifer Lea, director of client training and performance coach at the Johnson & Johnson Human Performance Institute, stressed that your body performs better when it has food for fuel. Without fuel, your body will break down stored fat, but it will also break down protein, reducing your muscle-building ability. She concluded that, overall, this does you a disservice, since muscle mass is important for healthy aging, performance, and metabolism. Instead of fasting before exercise, Lea recommended:

• Eating within two hours of exercise, ideally carbs and a little bit of protein—think a banana or a slice of toast with a thin spread of peanut butter.
• Experimenting with timing to find what works for you. Some people feel fine with a small snack right before a workout, while others need time for their stomach to settle after eating.

Source: Healthline