If that interests you, I recommend looking into gut health in general.

There is a lot of new evidence coming out that suggests that the bacterial makeup in our gut has a huge influence on the production of serotonin and some other hormone that influences our levels of happiness. I think the gut produces 90% of your bodies serotonin levels. I would recheck that stat but it definitely has a huge influence on your body and mood.

I used to ferment vegetables in order to introduce a diverse group of healthy bacteria to my gut. From my understanding, when you ferment them on your own, the bacteria created are as good as the highest quality probiotics on the market.