When you have diarrhea, why do certain foods like tomatoes, mushrooms and lettuce end up in your stool?

When you have diarrhea, food passes through the digestive tract too quickly, so some of the harder-to-digest foods survive the digestion process and end up in your stool. 

With diarrhea, the stool is usually too liquid because the intestinal walls are either irritated by the presence of a bug or reacting to a food intolerance.

The first situation is usually a one-off thing, unless you’ve picked up an intestinal bug while travelling down south.

In the case of food intolerances, it is important to find out which foods are to blame. If you have diarrhea or overly soft stool, try to remember what you ate in the past 24 hours and take note of it.

Once you determine which foods are irritating your bowel, eliminate them from your diet to give your body time to recover.