I use Perpetuem for supported centuries, marathons and long (20+ mile) marathon training runs. I try to minimize my soy intake - especially isolated soy protein - so the only time I use Perpetuem is when I know I won't be able to get protein at a store. It does supply my protein needs over a long run or ride.

There are also whey-based protein supplements, but I can't use those and expect to perform at all.