it could take a few days to affect him. Celiac disease can be identified through a blood test, but it is not 100% certain. Absolute certainty requires a biospy, I think. Basically, if you have have celiac, then the consumption of gluten (wheat, barley, etc etc) can over time cause perforation and permanent damage of the intestine. I have had a friend with celiac who was extremely and instantly bothered by ingesting gluten, and another who was completely asymptomatic except that she was always exhausted and could not gain any weight. It often goes hand in hand with lactose intolerance. I think it would be worth verifiying.