I eat carbs and whey protein while exercising, and as long as my intensity is high enough it seems like they get burned off. The real test though is controlling cravings afterwards - i.e. not stopping at three 7-elevens on the way home for cookies and ice cream.
It seems that when I eat stuff like plain oatmeal with plain whey protein drink, I don't get cravings as bad as when I eat sugary fruit like bananas or oranges.
So, I guess the advice is to be mindful and monitor your own cravings after cravings exercising and the day after. It's helpful not to berate yourself for going off the wagon, but to be analytical as to what kinds of foods set you off.
At least with me, the real damage is not what I eat DURING the time I exercise, but what happens to my diet afterwards.