While researching, I'm discovering what Rainman already knows and is patiently attempting to explain in another thread currently exploring this subject. That being that undigested food may be expelled without contributing much by way of growth to the fish. I THINK this is encouraging, as it may imply that the processed feed is purged, rather than just laying in the stomach, undigested.
On the other hand, this MAY also support the hypothesis that winter feeding provides very little benefit to certain species of fish, most notably warm water species. Even if they are willing to feed, cold water inhibits or at least depresses digestion, and undigested feed is simply expelled.
This tidbit also came from "Bluegills, Biology and Behavior", by Stephen Spotte.
