I would think that a high carbohydrate diet would make it worse. I also have SIBO and the bacteria that is in the small intestines feeds on carbohydrates making symptoms much worse. I can only function on a low carb diet but if he can’t have fat then I’m not sure what he can do since a low-carb diet is mostly protein and fat. Right now I’m on a two week Vivonex diet which is supposed to starve the bacteria in the small bowel. I had two rounds of antibiotics that didn’t help so hopefully this will. Vivonex is an elemental food formula that consists of completely predigested proteins, fats and carbohydrates. The carbohydrates are in the form of glucose that is readily absorbed high up in the small bowel so there is little left for gut bacteria to feed on.A good book that I read about this is “A New IBS Solution” by D. Mark Pimental ( Director of the GI Motility Program at well respected Cedars-Sinai Medical Center in LA) http://www.amazon.com/New-IBS-Solution-Mark-Pimentel/dp/0977435601/ref=sr_1_1?ie=UTF8&s=books&qid=1276727836&sr=8-1-spellI have heard that the Specific Carbohydrate Diet has helped some people so it wouldn’t hurt to try.