Diet change. 1 avocado/day. dark chocolate and same flavor ice cream everyday. running changed to 2 mi from 4, 3x/wk. black stool last 4days. related?

Not likely: The color of the stools can certainly be affected by the type of food that we eat, but usually not black unless you eat raw red meat or other dish containing animal blood. If you are really having jet black and tarry stools, then it may suggest bleeding inside the stomach or small bowels. You need to see your doctor right away for urgent evaluation.