I agree with the low sugar and organic recommendations. You'll also want to avoid any low carb versions that contain sugar alcohols as they could really upset his digestion. Rather than just focusing on protein bars, you may also want to consider a high quality whey protein isolate or egg white protein shake mix. Real food sources are superior to both of these, so he should also increase his intake of lean meats - especially white meat of chicken or turkey and fish - and eggs. Dairy's a good protein source IF he can tolerate it. Many IBDers have problems digesting it, either because of lactose intolerance or problems with the dairy protein, casein.
Diagnosed with ulcerative colitis spring 1999.
Maintenance dose sulfasalazine.
Probiotics, l-glutamine and fish oil caps. George's aloe vera juice. Oregano oil antibiotic, antiviral, antifungal. Long-term remission with only minor blips.