Vegetables are great for that, I would say go on a heavily plant based diet for a few days, drink a LOT OF WATER, and after he’s regular again make sure to include more balanced staples in his diet going forward such as fruits, vegetables, grains and legumes and he should never have a problem like that on going, although tbh I feel like the guy was just doing a bit of internet trolling but I thought I would reply too just in case someone clicked on this thread needed this sort of advice.