Many people notice their stool color changes after eating certain foods, and blueberries are a common one that can lead to a darker appearance. This observation is often normal and generally not a cause for concern. The temporary shift in stool color is a harmless reaction to the fruit’s pigments. Understanding these dietary influences can help distinguish between normal variations and changes that might warrant medical attention.
How Blueberries Influence Stool Color
Blueberries contain natural pigments called anthocyanins. When consumed, these pigments travel through your digestive system, and since not all compounds are fully absorbed, these colorants pass into the stool.
The typical brown color of stool comes from bile, a yellowish-green fluid produced by the liver that aids in fat digestion. As bile moves through the intestines, it undergoes chemical changes, gradually shifting from green to brown. The unabsorbed anthocyanins from blueberries can mix with this bile and other waste, leading to stool that appears darker, sometimes even black or with a bluish tint.
Other Dietary Factors Affecting Stool Color
Many other foods and supplements can alter stool color. For instance, consuming large amounts of black licorice, beets, or blood sausage can result in very dark or black stool. Dark artificial food colorings in processed foods and drinks can also tint stool.
Medications and supplements also cause stool color changes. Iron supplements, commonly taken for iron deficiency, can turn stool a dark green or black color due to unabsorbed iron. Bismuth subsalicylate, an active ingredient in some over-the-counter stomach remedies, can react with sulfur in the digestive tract to produce a black appearance. Activated charcoal is another substance that can make stool black.
Understanding Concerning Stool Color Changes
While dietary changes often explain dark stool, black stool can indicate a more serious underlying issue. Medical professionals refer to black, tarry, and foul-smelling stool as “melena,” which suggests bleeding in the upper gastrointestinal tract, such as the esophagus, stomach, or upper small intestine. The blood turns black and tarry as it is digested during its journey through the GI tract.
Conditions that can cause melena include peptic ulcers, severe inflammation of the stomach lining (gastritis), or esophageal issues like swollen veins (varices) or tears. Tumors or cancers in the upper digestive organs can also lead to bleeding that results in black stool. It is important to monitor for other symptoms accompanying dark stool.
Seek medical attention if black stool is tarry, has a strong, unusually foul odor, or persists beyond a day or two after consuming dark foods or supplements. Accompanying symptoms such as abdominal pain, fatigue, dizziness, lightheadedness, shortness of breath, or vomiting blood (which may look like coffee grounds) are serious signs. Consulting a healthcare professional is important to determine the cause of the stool color change and to rule out any serious medical conditions.