I don't know anything about its nutritional value, but if he took it, it can't be all bad. Try some frozen shrimp and / or scallops from your local grocery store. I buy mine in one pound bags at wal-mart for $7.99. They last for a while and the seafood is individually frozen making thawing easy. Biff the bimac likes both of them. I hand feed him ocassionally, when I have the time. When I offer him food by hand, he always grabs me and ignores the food. He'd rather tug on and explore my hand than eat. I'll let him do it for a while, but eventually pull my hand out. The last couple of times he followed my hand until he was almost completely out of the tank, spit water at me, and then let go. He's got a very interesting personality and he's fantastically curious.
I also offer him live crawdads when I can get them, or fiddler crabs if I can't get crawdads. (Crawdads are about half the price and have more meat to them, it would appear). Biff eats two crawdads or three fiddlers, or 1-2 small shrimp or most of one large scallop a day. I bought him about 6 weeks ago, when he was about 6" from the tip of his mantle to the end of his tentacles. He is now 8" long! He has a 120 g Oceanic home with a 35 gal sump, and he has littered the tank with shells!