As someone else mentioned, it’s the lack of fiber in so many US folks diets. When we finally get more fiber than they are used to, they tend to poo a lot. The food itself is fine for fast food.

I used to eat at Taco Bell on a near daily basis because it was my favorite fast food, cheap, and in the mall I worked in. I have never once had bowel discomfort from the food there. Even now, I ate it a few weeks ago, no problems at all.