Red wine can temporarily cause stool to appear reddish or darker due to natural coloring compounds found in grape skins. Since these pigments are poorly absorbed, they pass through the digestive system relatively intact. This change is typically brief, resolving within a day or two after consumption stops, and is not a sign of internal bleeding.
How Red Wine Pigments Survive Digestion
The deep, rich color of red wine comes from anthocyanins, which are water-soluble pigments found in the grape skins. When consumed, these pigments travel through the upper gastrointestinal tract, encountering various digestive enzymes and acids. However, these complex molecules are poorly absorbed across the intestinal lining into the bloodstream.
A significant portion of the ingested anthocyanins remains in the digestive tract, traveling through the stomach and small intestine relatively intact. Only about 1% to 2% of the total amount is absorbed, leaving the rest to continue toward the colon. These highly pigmented compounds retain their color as they mix with the forming stool mass, imparting a reddish-brown or dark maroon tint.
Visual Indicators and When to Seek Medical Advice
When red wine or other pigmented foods cause discoloration, the stool often exhibits a subtle reddish-brown or purplish tint that is mixed uniformly throughout the waste. This harmless color change disappears quickly, usually within 24 to 48 hours after the dietary cause is eliminated. The appearance is distinct from the visual indicators of actual gastrointestinal bleeding.
Bleeding from the lower gastrointestinal tract, such as from hemorrhoids or an anal fissure, typically results in bright red blood that may be seen on the toilet paper or streaking the surface of the stool. Conversely, bleeding originating higher up in the digestive system, such as the stomach or small intestine, often results in a black, sticky, or tarry stool known as melena. This happens because the blood has been chemically digested on its way through the tract.
It is important to seek medical attention if red stool is persistent, meaning it lasts longer than a few days, or if you have not consumed any known pigmented foods. Immediate consultation is warranted if the red or black discoloration is accompanied by other physical symptoms. These concerning signs include abdominal pain, dizziness, weakness, vomiting, rapid heart rate, or a noticeable change in the consistency of the stool, such as persistent diarrhea.
Other Common Dietary Causes of Red Stool
Many other common foods contain natural or artificial pigments that are also poorly digested and can temporarily mimic the appearance of blood in the stool. Beets are one of the most frequent culprits, containing a strong pigment called betacyanin that can turn urine and stool a pronounced red or pink hue. This effect, sometimes called beeturia, is entirely benign.
Highly concentrated tomato products, such as large servings of tomato soup or paste, may also contribute a reddish cast to stool. Furthermore, various items containing red food dyes, like certain red-frosted baked goods, brightly colored cereals, or gelatin desserts, often contain pigments that survive the digestive process. These instances of discoloration are temporary and represent undigested color compounds rather than a medical concern.