The gut biome changes or responds greatly to what sort of foods one is eating, and just changes in the biome in different areas of the gut can cause one to feel sick, but generally settles as the body adjusts to a different diet or schedule.
However if it's important to you for real insight, doctors and specialists in the field are a safer shot - I'm presuming the average doctor/ diet specialist over your way is a lot more competent than what I seem to get stuck with here in my neck of the woods. [1]
Though a little off topic, issues with food additives are worth noting. Food manufacturers are also changing what they add to foods, eg to avoid higher sugar content, using things like inulin which for myself from sweet potatoes was never a problem, the cheap nasty BS that's a form of inulin added to some food wraps caused me misery and consequently sensitised a reaction to sweet potatoes for a time. I also found out the hard way, not quite 10 years ago, certain food intolerances can exasperate other possible food related conditions that form a best fit for self diagnosis - so after a couple of stints doing my best to dodge gluten for a a year or so which did seem to help a little ... quite accidentally discovered many people suffer due to the long used 160b food additive, as symptoms were a really good fit and then avoiding 160b, that was my main gut dilemma I could recall suffering from an age of roughly 6. Also after a time I was back to eating regular bread without much of an issue.
[1] Presently ongoing but primarily unconfirmed gastroparesis / gastro-paralysis given the symptoms / debilitating outcome including some BADAS symptoms