I had to start supplementing with psyllium fiber (powder) several months ago after a massive hemorrhoid attack last fall. (Surgeon gave me the identical advice.)
If I don’t get at least 40 g a day of total fiber (about 20+ of which are the powder), stools get large ‘n’ hard. It’s working, and my ass is thanking me.
What I’m having trouble squaring is I don’t think we evolved eating that much fiber every day. Pre-agriculture it would have been (depending on which part of the planet) lot’s of animal protein and whatever roots & berries you could find, right?