I used to get killer trots from fast food too, until I figured out that it was the ARTIFICIAL MAYONNAISE!!
I can eat real, fresh mayonnaise, though I prefer Miracle Whip, but fake mayo is truly BBAADD!! How do you MAKE fake mayo, anyhow? NO, I DON'T WANT TO KNOW!!
Just my personal experience with BK, Subway and Wendy's. Mayo on = lotsa time in the little room. No mayo, no problem.
I am not familiar with fake mayo. My BK hamburger had mustard, no mayo. The trots continued for about 4 weeks, gradually being less and less. THAT is not normal for getting bad food but I don't know what it was. I had something similar many years ago that I caught in Switzerland but it was even worse. I haven't been back to Switzerland either. LOL