I live in France, a country that has built its reputation, tourist industry and just about everything else based on white flour, cream and sugar.
We have a very low rate of UC, obesity and gut diseases. Not that they do not exist (especially since fast food outlets like Mc D's and Pizza H and KC have moved into town) but they are substantially lower than what you find in the U.S.
We eat baguettes with white flour at every meal, rarely if ever use sugar substitutes (usually only the overweight people do here...which means that it is even rarer than you may think), have a much lower consumption of sodas and much, much smaller portions of everything.
WE do not SuperSize food, we Undersize it here...The smaller the better, the more refined the better (I used to think that they were giving out samples to taste and wait for the 'real ' meal to arrive only to discover that I had just eaten it in 2 bites. (no joke!)
They are huge coffee drinkers but seem to forget to add water ...again the smaller the better. Less is best.
Most milk products like cheeses and yogurts used to be made with raw milk (we still find about 20%) which contributes to good gut bacteria and lower rates of gut disease...we have a lot less bacterial outbreaks than you could ever imagine. Better immune systems too.
So it may not be so much about what you eat but how you eat it, how it was grown and how much of it you eat.
I am learning. It has taken years. I eat small. Carefully. No gulping soda or slurping sugar but I do enjoy good ice cream (it is all good) and tasty pastries. They do not make me ill...They make me happy
As for the autoimmunes, I was born with them, did not acquire them...They are part of my genetic code. No sugar will not change that fact.