My twin brother was born by caesarean. He gets asthma attacks from allergies that I don’t have. I’ve wondered for a while what effect a faecal transplant could have...
Anecdotally, I am Norwegian genetically, and it has been said that the scandanavians are the group that developed the gut biome to be able to eat cheese/dairy - and I eat a TON of cheese each year (and I suffer no ill affects (I’m super lean and tall and skinny))
Whereas one of my exes was Asian and would get IBS whenever she ate cheese.