Well, yes. Reduced-fat yogurt is more watery and quite a bit thinner than the full-fat stuff. You'll find, first and foremost, that your fro-yo is icy rather than creamy. In full-fat yogurt, the extra fat replaces the water—fat freezes very differently. Deliciously differently, in fact. You'll also find that reduced-fat frozen yogurt will freeze into a solid block very quickly.