"An apple a day keeps the doctor away". We've all heard it, but not many people know where or why that saying exists. I'll tell you: apples contain malic acid, and malic acid helps soften and break up gall stones, keeping bile flowing more freely through your lymphatic system. The lymphatic system includes your liver and your lymph nodes and is hugely responsible for clear out cell debris, metabolizing fat and removing toxins from your body.
When I have my clients do a liver/gall bladder flush, on top of having them take a malic acid supplement, I also have them eat an apple a day. :)
Just a tip: apples are sprayed heavily with pesticides, so you should ALWAYS buy them organic, and wash them with a fruit and veggie wash to remove any waxes or residues.