That sounds incredibly hard to manage. You have my sympathies. I think finding a good dietician versed in IBS would be essential for short and long term management as most doctor's don't have enough training in nutritional support.

Luckily for humans, as omnivores, we can exist and survive on a wide variety of diets. Our bodies can make muscle from fat and carbs and most foods (even potatoes) contain protein.

Since you posted to ask -- I'd suggest using an app like "food allergy detective" to get a better list of what's tolerated (I know IBS isn't the same, but the app's a symptom tracker) and as for the trying to get more antioxidants, I'd talk to a dietician about what sweetmeats (organ meats) may be tolerated if you're open to trying them. Sweetmeats are way more nutritious than muscle meat and can have more vitamins, etc. than vegetables and fruits. It's why many hunter-gatherer societies can survive and thrive.