The "why" is twofold:Originally Posted by salsabike
First, if you want to be able to utilize the calories you just ate, it takes up to three hours for you to fully digest them.
Second, when you digest food, a higher volume of blood moves to your internal organs to aid in the digestive process. When you exercise, a higher volume of blood moves to your working muscles (in this case, your legs). Can you see the conflict there? Unfortunately, your performance will be compromised AND you'll probably get an upset stomach, stitches, or cramps.