What is the number one food that causes diarrhea?

Could you please elaborate on what specific factors contribute to a food being the number one cause of diarrhea? Is there a particular type of food, ingredient, or preparation method that consistently triggers this condition? Additionally, are there any underlying health conditions or individual differences that might make someone more susceptible to diarrhea from certain foods? I'm interested in understanding the science behind this question and how to best avoid potential triggers.