Wouldn't recommend fasting for HIIT or any super intense activity, but the long runs may improve. I'm saying this since sugar is a lot quicker to be transformed

Wouldn't recommend fasting for HIIT or any super intense activity, but the long runs may improve. I'm saying this since sugar is a lot quicker to be transformed into energy by the body than fat. But we're all different, so, you could give it a try :).