I believe that some of the cultural trends have caused a lot. There's strong evidence that antibiotics and antibacterial-everything overuse (reduce microbial exposure) results in increased sickness, increased asthma, rash, allergies, and autoimmune disease. (Celiac is an autoimmune disease).
I have a chronic illness so in finding answers for my health, I see a lot of other people with the same and many autoimmune comorbities. Oh my! There's a whole world, and yes, "who can be the sickest" is definitely happening. It's crazy. People who claim they cannot tolerate any medications (research demonstrates that people who claim this are especially susceptible to nocebo effect and benefit from therapy). People who eliminate everything and anything from their diets and grow increasingly less able to eat a variety of food.
Which brings me to the other. New research (like 2015) says that food allergies should be treated with exposure - especially before 18 months of age. What advice have new parents been given for years? Don't give any potential food allergens until after 1 year, or after 2 years if there is food allergies in the family. Uh. i think we have a reason for increases in food allergies?
Then there's that whole separate issue of "non-food" ingredients in the food that the masses consume. Perhaps.... it's not about the organic label and more about reducing the "chemical" food additives. But placebo/nocebo effect is strong and once someone believes it's the "pesticides" or whatever... good luck convincing them otherwise.
My dad has undiagnosed digestive problems that improve by eliminating gluten. My mom went gluten free too. She started talking about how much better she felt too. Uhh... maybe she felt better because they had stopped eating lunch at McDonald's everyday? My dad's GI troubles didn't end by going gluten free - they only changed. I suspect he has IBS and needs a low-FODMAPS diet. The reason I expect this is because the carbohydrate portion of wheat (fructans) can be an irritant when consumed in large quantities, but they're also in other foods that are hard to eliminate like onion and garlic.
We (as a population) eat a huge quantity of potential-irritant foods and non-foods, all driven by mass agriculture and the constraints of modern society. I wonder how it all plays out. i don't see many happy endings in the next hundred years, unless the back to nature movement becomes huge... or the population declines. IDK. It's unsettling. I try to stop myself from worrying and grow my own food and not buy into all the chronic illness BS.
Not that chronic illnesses are BSy. The one I have is not life threatening or life shortening, but so many people with it are running to the ER over "normal" symptoms that are not an emergency - just uncomfortable. Dare I say "get used to it" "Learn to deal with it" "it could be a heck of a lot worse". "What do we really have to whine about" ???