Black stool, medically known as melena, is a noticeable and often alarming change that signals a potential issue in the digestive tract. While true melena is a sticky, black, and foul-smelling sign of digested blood, the initial concern often arises from dietary changes. Many people who notice a darkening of their stool immediately wonder if a recent glass of red wine or other dark food is the culprit. Understanding the difference between this benign color change and a serious medical issue is important for knowing when to simply wait and when to seek professional medical attention.
The Role of Red Wine Pigments
Red wine can certainly lead to a temporary darkening of stool color due to its natural composition. The deep, rich color of red wine comes primarily from compounds called anthocyanins, which are potent pigments found in the skin of dark-colored grapes. These pigments are not fully broken down or absorbed during the digestive process as they pass through the gastrointestinal tract.
When a person consumes a significant amount of red wine, the concentration of these residual anthocyanins in the gut increases. These unabsorbed pigments can then tint the stool a very dark red, deep purple, or dark brown color. This pigment-based darkening is harmless and typically resolves within a day or two once the wine has cleared the system.
Non-Wine Dietary Sources of Dark Stool
Many other common items besides red wine can cause a harmless, transient darkening of stool that may be mistaken for melena. This darkening is temporary and not indicative of internal bleeding.
Medications and Supplements
Certain over-the-counter medications and dietary supplements are frequent culprits in this phenomenon. The drug bismuth subsalicylate, a common ingredient in remedies for indigestion and diarrhea, reacts with trace amounts of sulfur in the digestive tract to form black bismuth sulfide. Iron supplements, frequently taken for anemia or during pregnancy, are another very common cause of dark or black stool. The iron not absorbed by the body is excreted, giving the feces a dark, sometimes greenish-black, hue.
Dark Foods
Furthermore, several dark-colored foods contain pigments strong enough to temporarily alter stool color. Eating large quantities of these items can result in a harmlessly dark bowel movement.
- Black licorice
- Blueberries
- Blood sausage
- Beets (which can contribute to a dark appearance)
Serious Medical Causes of Black Stool
True black stool, known as melena, is a medical finding that requires serious attention because it indicates bleeding in the upper gastrointestinal (GI) tract. The stool is black because the blood has been exposed to digestive enzymes and stomach acid for a sufficient amount of time, turning the hemoglobin a dark color. Melena is characterized by a shiny, sticky, tar-like texture and a distinctly strong, foul odor due to the breakdown of blood.
The most common cause of melena is a peptic ulcer, which is a sore in the lining of the stomach or the first part of the small intestine. Other upper GI sources include gastritis, which is inflammation of the stomach lining, and esophagitis. Excessive alcohol consumption, including heavy wine intake, can directly contribute to these serious conditions. Chronic or heavy drinking can severely irritate the stomach lining, leading to gastritis or even acute hemorrhagic erosive gastropathy. In individuals with liver disease, alcohol can also contribute to the formation of esophageal varices, which are enlarged veins that can rupture and bleed profusely, causing melena.
When to Seek Medical Attention
While temporary darkening from wine or food is benign, true melena is always a symptom that warrants a professional medical evaluation. If the black stool is definitively tarry, sticky, and has a strong, unpleasant smell, it should be investigated regardless of recent diet. Stool that remains persistently black for more than a day or two after stopping the consumption of dark foods or supplements needs medical attention.
It is especially important to seek immediate medical care if black stool is accompanied by other physical symptoms. These warning signs include vomiting blood or vomit that resembles coffee grounds, which is another sign of upper GI bleeding. Feeling dizzy, weak, or lightheaded, along with a rapid heart rate or shortness of breath, can signal significant blood loss that requires urgent assessment.