My Weight Watchers leader says that exercising before breakfast kickstarts your metabolism.
I'm not a fan of fasted exercise at all.
Unless you're going for that soft look, lol.
Nothing is really going to 'jumpstart' your metabolism. And eating before exercise a) allows you to work at a higher intensity which at the end of the day matters most and b) gives your reason not to waste muscle (hence that soft comment above)
Ive read many things that have said that doing low intensity exercise (heart rate 60-65% of max) will not use muscle for energy, depending on your body type, and I doubt many people here would be ectomorphs.
because everyone is different.
I've also read that a cup of coffee before a cardio workout gives you a little more endurance (but that makes me -ummm - oh how shall we say this politely - that makes me need to take a breakmidway thrumyworkout...)