Celiac is an auto-immune disorder, an allergy. Celiac sufferers who consume even small amounts of gluten will have their digestive system more or less shut down

Celiac is an auto-immune disorder, an allergy. Celiac sufferers who consume even small amounts of gluten will have their digestive system more or less shut down for a period of up to several days afterward. Gluten sensitivity is similar to lactose intolerance (and is closely related to FODMAP sensitivity and IBS), for those folks consuming gluten leads to digestive problems. Just as many people with lactose intolerance can consume some lactose if they are careful the same is true for many people with gluten sensitivity, but also the severity of symptoms vary greatly and some people find that playing russian roulette with their gut is too dangerous so they seek to eliminate it from their diet entirely.