I don't want to hijack this thread but thought I might just offer a slight insight into our situation, although be warned there are graphic poop descriptions to follow. My feeling is that gluten intolerance is the latest fad illness. Celiacs disease is a real condition and has been recognised for a number of years. For those that are truly gluten intolerant it is an awful complaint. As for what used to happen to people with intolerances and/or allergies in an earlier time I would say that as babies they did not thrive and may well have had a shorter life span (depending on how far back in history you wish to go.) As adults they would have been constantly ill and would have been considered sickly. Our own situation is a little different in that our 18 year old daughter has multiple food allergies which were diagnosed at 9 months of age by a paediatric allergist. She is allergic to wheat (note, that is wheat and not gluten), potato, barley, dairy, eggs and dogs. The Dr suggested we get rid of our dog but we pointed out we had the dog before we had the baby so that stopped that conversation there. We have found she can eat Spelt and Kamut flour due to their shorter protein chains. Anyway, I digress. From day 1 it was clear DD had a problem as she cried after eating (she was breast fed for 15 months) and developed eczema all over her body. She had to have clean sheets on her cot every day due to the amount of blood on the sheets from where her wounds had broken open and bled while she slept. Her poo (sorry to get graphic here) was something to behold as it was so dense that it was in balls and if they accidentally rolled off of a nappy they actually bounced! Our daughter was being 100% breast fed and our doctor just kept getting us to try cream after cream after cream and we spent an absolute fortune. One day we ended up seeing a different doctor who sent us to a paediatric allergist who changed our lives. He diagnosed DD's allergies and told me to remove those foods from my diet as she was receiving the proteins via the breast milk. I immediately changed my diet and it was like a miracle had happened. Within 24 hours all of the eczema on her body, except for one small patch on an ankle, had disappeared and at 9 months of age she finally smiled for the first time in her life, yep, there had been no smiles to that point which I am guessing is because she was in constant pain. 18 years ago trying to get any sort of food stuffs that fitted with her allergies was impossible but luckily I have always like to cook. I learned very early to read ingredient labels on absolutely everything.
Although DD is now 18 years old, she still has not outgrown her allergies and has them for life. If she eats things she should not she will break out in eczema within a matter of hours.
So, in answer to your question of what happened to people with intolerances and/or allergies (because they aren't the same thing) in an earlier time, I think we can look at my daughter's experience and say they simply did not thrive and, in a more extreme case and an earlier time period, would have died.
Enough of being a negative Nelly and back to the discussion of soap and all things soap related.