Dunno man, I eat a lot of salad, only brown bread and pooh at least once a day – my GF says I’m weird.
Never get them, but realistically I guess they’re caused by eating food that is mostly digested and therefore you’re only left with dense residue. When I was in Greece, with all the white bread I felt awful, permanently needed to go but couldn’t – it was like passing stones.
A friend of mine turned up at my ol’ place in London once with the same problem, hadn’t been for a week. I fed him lots of water, and then 6 weetabix followed by about 200mL of Olive Oil. Worked in about an hour.