There are many causes of diarrhea including but not limited to prescription drugs, parasites, allergies, lactose intolerance, celiac disease, sorbitol, mannitol, and sulfites.  Sulfites are frequently use as anti-browning agents for potato products.  Other products that have sulfites include some candies, coconut, sodium metabisulfite, dried fruit, wine, beer, canned vegetables, soup mixes, maraschino cherries, molasses, and some vegetable juices.

Apple cider vinegar (and better yet certo) are good cures for diarrhea because of the pectin they contain.  The pectin creates a protective coating on the lining of the intestine which helps protect against irritation.  Diarrhea can frequently be caused by nasty microorganisms and apple cider vinegar can take some of them out.

Weirdly enough many claim coconut macaroons as being a cure for diarrhea and chrohn's disease.  Another 'folksy' remedy popular in Brazil is milk and cinnamon. 

Other tricks include carob powder, berberine, tannins (such as geranium root), and peppermint oil.