Brad Pillon the author of Eat Stop Eat (my favourite book on intermittent fasting) has a good little blog post about this today : Fasting Exercise and Blood Sugar
Did you know that when scientists studied people who exercised after fasting for 23 hours, their blood sugar levels were actually found to be slightly higher then when the same people exercised after a small meal? (Coyle EF 1985; Dohm LG 1986)
I was at a Krav Maga class on Monday when one guy threw up after the warm up. It was a moderately tough session but not that hard. I think the problem usually is when people have eaten too close to exercise. Would he have chucked if he'd been fasting?