Subbing - out of self-interest!
I hate to say this, but I'm over 40 and
frequently have the same problem everyone here is describing in their babies.

I even have trouble with things like lettuce (though sometimes I'll have long stretches with no issues.)
Sometimes I will do better for a while if I'm using any kind of "probiotic" at all. Yogurt cups from the store even do the job, I don't have any confidence in anything staying undisturbed long enough to make my own (3 cats and a 2 yo grandson in the house.)
If I'm having trouble with fruits and veggies - I like many, but during a harsh time the acids will make my inner ears/mouth/throat tingle, and the food looks the same flushing as it did swallowing. Once I was so far chemically off kilter that my hands were turning red and getting bleeding cracks when I was peeling and cutting up potatoes for others to eat - not a huge amount, just family dinner for DH and two growing kids, I knew I couldn't have them. It freaked my dc like crazy. I know cooking destroys some nutrients, but cooking those things like apples or pineapple help alot, or putting juices into something that will be cooked. I have found quite a few recipes over the years, I think the cooking breaks down some of the acids and other things. When it comes to grains, beans, lentils, corn, and other seed foods that have a distinct skin, sometimes I can eat them if I run them through a blender after cooking to softness (I don't care if my bean broth is cloudy instead of clear!) Sometimes things go ok, and I can eat stew with everything I want, and a measure of barley soaking up alot of the broth! Other times I will simmer beans to a point of perfection, make my cornbread, and not get any value from either.
I'm quite certain mom weaned us all early, no telling if that is a contributing factor or not. I do know my older sister is permanently non-dairy now due to severe milk allergy -but went as long as she could with yogurts and cheeses. Younger sis was allergic to dairy as an infant, but can eat dairy foods now.
I keep trying different things, but I would love to get this nailed down.