

What you feed grows.
Different microbes like stuff like beans or vegetables more than red meat and sugar
It’s why people that eat healthy get the shits from one fast food meal, but someone who eats that daily is fine. And while fast food guy can’t stop farting after eating beans, but a vegan is back to baseline farting.
Selection bias…
A frightening amount of people get married because they’re worried about having someone to take care of them at an elderly age. Even if their goal is recipical, for a lot of people that’s a big driver for marriage.
People who are more self sufficient and with a strong family health history doesn’t have that drive.
Couple that with not being able to “offload” tasks to a spouse and you end up with single people staying active mentally which is one of the biggest negative correlations to Alzheimer’s.