1 month
Because your garden variety unhealthy american who survives off fast food and takeout eats very, very little fiber. So they eat something with beans in it and they are totally unprepared for a significant amount of fiber.
I’ve also heard theories that because it’s already in little pieces people don’t chew it well, which also will upset your stomach.
Definitely start with The New Order. If it doesn’t run well for you (it is a bit jank) play The New Colossus.
TNO, TNC, and The Old Blood (TOB?) Make up the modern rebooted trilogy. They are sublime even if there’s some technical jank until you make it to TNC. If you want more after that, try Return to Castle Wolfenstein. It is very old but very tightly designed.