What could cause problems metabolizing starches?

My son (age 10) has been battling a digestive/GI tract problem for a few weeks now; his physicians are a bit stumped on what the cause could be and they are in the process of scheduling more tests and labs. He’ll be going through a GI workup next week (ultrasound, upper GI, possible endoscopy). He’ll also be meeting with a peds GI specialist.

I know that his doctors are working on this, and I'm confident that they’ll figure it out, but in the meantime I'm trying to figure out what to feed him. His symptoms don't seem to point to any one thing, so they don't really have any advice to give me. I'm not going to take advice on here as gospel medical advice of course, but hoping you all might have some ideas.

He had a virus a few weeks ago (as evidenced by white counts), which caused his lower intestine to relax to the point that it totally stopped. The treatment that he was given to get it going again was too harsh on his system and caused him to vomit several times per day. We’ve that under control, but over the past week and a half he has only been able to keep down liquids and soft foods - anything beyond that makes him cramp up and vomit. I've been keeping him on liquids like water, Powerade (for electrolytes and some calories), juices, and broth. As far as foods, he's been on yogurt, soft fruits, smoothies made only with fruit, juice, yogurt, and raw honey, mac and cheese (comfort food), and potatoes. This week we started adding in some bread.

When we started adding in bread, he said that he felt like “his skin was on fire” and parts of his body itched horribly. This lasted for 30-45 minutes. When he has potatoes and bread in the same meal, he has a similar reaction, but with abdominal pain as well. However, if I give him potato soup (made with homemade veggie broth and milk), he doesn't have that reaction, so I'm thinking that it's a reaction to too much starch. (We realized this after his doctor's office shut today, I'll put a call in Monday morning to let them know.)

I'm moving his diet to one that's more fruit and vegetable based and hiding starches from him (he forgets and grabs a piece of bread); however, I feel like I'm taking stabs in the dark. The only medical care available in our area over the weekend is the ER, and I really don't want to take him in there unless it's necessary. (He has a lowered immune system due to a rough bout with SARS a few years ago, and with him being sick, I'd rather not have him in that environment.)

Any suggestions or sites where I can research this would be greatly appreciated. Again, I'll research out any recommendations before trying them, but I don't even know where to look.

Thanks

Im not a professional, and im no way able to give dietary advice on this matter as im only a personal trainer, not a dietitian!

heres what i can see…. all you have been feeding him basically is carbs.. he is not going to be burning many carbs, he’ll be burning fat and muscle. i strongly recommend getting more protein into the poor boy. yoghurt would be the only real source of protein he has, and thats a poor source at ideal.. im not sure how you could give it to him, but i know he needs some! His body would be burning lean muscle for the ammino acids his not getting, so he needs some protein! its the building blocks of life, and your body needs plenty of it. it repairs.grows cells, helps with immune support, makes your blood clot, the bodys only source of nitrogen.. id strongly advocate more protein, how its delivered is up to you. a supplement if you and comfy with giving him that would be great! Comes in liquid form and is an excellent source. otherwise eggs, chicken meat etc. try some chicken soup, with egg whites in it maybe? i hope i can be of some help! Protein protein protein!