Guys, coffee is zero calories, right? The caffeine will help mobilize fat stores if you've got an empty stomach and it helps motivate you. Win, win. Still though, a little bit of milk and a small piece of fruit or something helps raise glucose and helps preserve muscle. But it's not that big of a deal if you're just doing some steady treadmill wlaking, etc. Serious intervals or something and you may need to rethink the empty stomach bit.