A lot of gut issues are a combination of:
Allergies to food. Diagnose and treat by cutting the most common offenders from your diet first: gluten, eggs, nuts, dairy. If there’s no improvement and you’re desperate, cut everything from your diet except rice and water, and add foods one-by-one until you isolate the culprit.
You may have an intolerance to food which isn’t an allergy, e.g. coeliac disease. These can be diagnosed by a colonoscopy.Allergies to other things in the environment that are causing issues, e.g. fragrances.
SIBO (small intestinal bacterial overgrowth). Diagnose by doing a SIBO breath test, and treat with a combination of antibiotics for the initial cull, pre and probiotics until you develop a healthy flora, then be very wary of having antibiotics from then on.
SIBO is often caused by a hereditary inability to absorb a certain type of dietary sugar, e.g. fructose (fructose malabsorption) or lactose (lactose malabsorption). When eating foods containing that sugar, you don’t digest it, which leads to an overgrowth in bacteria which consume that sugar. Diagnose by doing a SIBO test, treat by avoiding that food and/or taking enzyme supplements to help you digest it.
(I don’t know any scientific basis for this point, but it seems to be this way from observation) There seems to be certain ‘types’ of people: red meat people, white meat people, no meat people or it-doesn’t-matter people. If your diet is heavily slanted towards one of the ‘types’, it’s worth trying out the other types to see if you do better on that diet.
There’s a few supplements which are generally useful, and good to have in the toolkit:
Slippery elm powder in capsule form is a great soother, forming a mucus-like material in your guts.
Activated charcoal capsules are useful for soaking up toxins in the gut, which is an issue experienced with SIBO-related bacterial die off. Be careful with over-supplementing with these, because it will soak up nutrients also.
Just a comment on writing for understandability — compare Benjamin Franklin, writing in 1750:
Shorter is (almost always) better, please don’t write things longly just for the sake of it!