Iron supplements are well known to cause dark brown stools. This can be alarming to patients, especially if the iron-deficiency is due to GI bleeding. It is important to discuss stool changes with patients when they begin iron supplements. Fiber does not affect iron absorption. In fact, iron supplements can cause constipation, so a high fiber diet may be helpful. Vitamin C helps iron absorption, as does red meat consumption. Dairy products, on the other hand, may reduce GI absorption of iron.