LOL! Sorry, no pun or insult intended. :-)
"More solid answer," I love that.
All I can tell you is that the small intestine functions to absorb most of the nutrients in food. Aside from diarrhea, you'll probably need to provide some form of vitamin and mineral supplements.
This is a great question to post to one of the veterinarians here at Med Help. I'm sure one of them will be able to give you a more solid answer. And best of luck to your pup!
Dogs have a pretty short gut, so I would not be at all surprised if removing 50% of it were to cause the type of symptoms you mention. I suggest asking your vet if your dog should be on a special food, and then feed cautiously. Play it by ear and see how close you can get him back to a normal diet. With this kind of surgery, I would be surprised if the vet did not provide detailed dietary instructions for you. If they were not given, ask.