Worms are pretty high in protien. If one were to only feed earthworms, but feed them in moderation as a fish may actually eat in their natural environment, it may be a decent diet to a purely carnivorous fish. Feeding earthworms as a regular diet on a daily basis would likely cause the fish to be overweight and lead to a shorter life span, just like with people. I don't have any scientific evidence to back this up, just my personal opinion.
I find that using live foods as a supplement and for conditioning for breeding works best. A good quality pellet, fed in moderation, is the best way to go. Based on the advice from several of our speakers over the years, I have actually cut back on feedings to 4-5 days a week.