You can find a healthy and fit person and get them to give you some of their gut flora and then eat it. That could probably work. It also might make you sick (I imagine) and it's terribly disgusting: "On a scale from swallowed to poo, how do you want my eaten food?"
So, takeaway from this ramble, do what your body responds well to, and keep to generally "good patterns" of hygene and balanced diet. Anecdotally, and from many practicing physicians, this tends to work out "ok" in the long run.
I've followed some of its advice and have been very happy with it.
The main takeaway is this: Fructose and glucose are easily absorbed in the small intestine, while complex carbs are not. Instead, they are fermented mainly in the large intestine, by bacteria that specialize on that over time. The problem might be worsened by insufficient stomach acid and digestive enzymes (e.g. weakened pancreas). If you have a microbiome that has tilted towards a non-optimal constellation, then you can do damage control by eating as few complex carbs as possible for a time. That means no sugar, no grains, no potatoes or rice, not even sweet potatoes or yums. The book also recommends to employ powerful probiotics (e.g. homemade yogurt that ferments for 24h). I personally have been doing water kefir for a time (which is a wild ferment, so a bit risky) and this helped my IBS a lot. I might take a ubiome test sometime and check what exactly is wrong with my microbiome.
If you go nothing else, make sure you take good care of your mouth, gums and teeth!