My stool has been very dark brown since yesterday? is this a cause for concern... i did eat spinach mostly was week and fish and blueberries?

Normal: Depending on your diet, normal stool can be soft or more firmly shaped, brown, light brown or green. See a Dr if you have stomach pain, or watery diarrhea for more than 3 days, with or without blood. Keep a food diary and see if you can identify the food or supplement that causes the dark brown color. Sometimes spinach or other dark green vegetables can cause this.