Our guts are extremely unique. what irritates one persons gut will be fine for another.
What works for me (and has reduced my ASD negative symptoms so so much) (This is not advice, just what has helped on a very confusing journey where ive tried EVERYTHING:
*No caffeine or stimulants - I drink decaf tea, decaf coffee, ive quit the ritalin (Ashwaghanda is a non-cardiac stimulant so it wont mess with anxiety but can help with energy and focus)
* no animal products - Dairy gave me a lot of issues, meat agitated my gut and emotions
*No sugars or grains - no fruits, grains, flours, wheat, no natural sugars like maple syrup or honey. No potatoes or starchy veg like sweet potato. Rarely I will have pumpkin.
* probiotic foods (not supplements) homemade coconut yoghurt, coconut water kefir, decaf kombucha, saurkraut, ACV (store-bought, but raw), kimchi
*Tumeric and ginger everything - the roots or dried spices: juice shots, golden milk lattes, tea, add to most dishes (anti-inflamm and soothe your gut)
Its basically a vegan version of the GAPS diet ("Gut and psychology syndrome"). Based on: Plant proteins (beans, tofu, nuts, legumes, fermented protein powders, bean flour) + non-starchy veg (cauliflower, broc, greens, celery, brussell, cabbage, carrots, tomato, salad veg etc..) + healthy fats (olives, avocado, coconut oil/cream, coconut butter etc..) + probiotic foods. I have a lot of slow-cooker vege soups and stews, stir frys, green juice, protein smoothies, salads, buddha bowls, protein+bean chocolate brownies, bean/lentil pastas, 90% or sugar-free dark choc etc..
Its been so helpful for me, but I know most people would find it too restrictive
Some youtubers who do similar (but not the same thing) are: theveggienut and healthycrazycool
I use these for inspiration but still stick to my own guidelines and just make swaps