What I'd like to know is which types of diets either inhibit/promote the growth of these bad bacteria. The types of bacteria in your gut being linked to parents or young age, might just be a symptom of learning your diet from your parents.
Specifically kefir/filmjölk. Buy a bottle, take a serving in the morning, and at night if you like/can afford.
I've turned my life around. Friends have stopped proton pump inhibitors/antacids like Prilosec/Omeprezole, etc, because of this simple lifestyle switch (one serving per day). I take many more.
If you have an instapot or yogurt maker, for $2.5, you can make a gallon of yogurt which lasts me about 1-2 weeks. I started my culture with a tub of Activia that my sister left in the fridge ~ a year ago.
Kimchi is also cheap to make yourself, although it does take a bit more prep.