When I did food allergy testing for my son, and eliminated those foods to which he tested as being allergic, and also eliminated food colorings and preservatives (Feingold), he stopped wetting the bed at night as one of many benefits.  The book by Dr. Doris Rapp, called "Is this Your Child?" has info on food allergies and intolerances, and on keeping food diaries.  Her theory is that the body tries to flush out irritants... just like when your nose runs when you have a cold...the bladder and urinary tract probably produce more liquid in an effort to flush away the irritant, and the item also possibly acts as like a "drug", by putting the child into a heavier state of sleep, so that they are less likely to wake up and use the bathroom. Thus, more accidents!

Pumpkin seeds are supposed to be beneficial for adults with urinary problems, and so is cranberry juice.  I believe that probiotics are also helpful, especially is there is a tendency towards having problems with yeasts, or blood sugar levels.