Can red wine cause black stools?

In this short article, we will provide an answer to the question “can red wine cause black stools?” and the reason behind this.

Can red wine cause black stools?

Yes, red wine may cause black stools. The reason for the black stools after drinking red wine is the low bioavailability of the red wine pigments, the anthocyanins (3).

The low bioavailability of anthocyanins causes low absorption of these compounds into the blood circulating system and a high excretion rate of anthocyanins in urine and feces, leading to the darkening of the stools.

The dark stools are also called black stools, as they differ from the usual color of stools, which is dark brown.

Why does red wine cause black stools?

Red wine can cause black stools because of the pigments present in the wine, which are derived from the grapes.

The diet affects the color of stools notably. The normal color of feces is dark-brown, however it may vary, depending on the individual’s ingestion. For instance, a large consumption of milk causes the color of feces to lighten, due to the increased amount of fat (1).

The pigments in red wine are anthocyanins, which are phenolic phytochemicals with an improved antioxidant capacity. Because most red wine anthocyanins have low bioavailability, these red pigments are eliminated in the urine and the feces (3).

The anthocyanins and their derivatives of red wine are methylated anthocyanin Peonidin that have the visible color magenta and the O-methylated anthocyanin Malvidin with the purple color. 

These red and purple pigments are not readily bioavailable to the body. As a result, their antioxidant action is prolonged and also part of these compounds are excreted, leading to the darkening of feces and urine. 

What other foods change the color of the stool?

Other foods that cause the change of the color that differ from the usual dark brown of stools are (1,2):

  • Cherries, licorice ice cream, foods containing a high quantity of iron, and the ingestion of charcoal cause black stools
  • The ingestion of large quantities of milk or a diet rich in fats causes the stools to lighten
  • A great ingestion of meat leads to the brownish-black appearance of stools, due to the presence of hematin and iron sulfide

What else can lead to black stools?

Black stools can have other causes rather than drinking red wine. The other possible causes of having dark feces are: 

  • Intoxication with calomel produces a green tinge, due to the reunion of mercaptan with mercury (1)
  • Deficiency of vitamin K caused by impaired nutrition or by therapy with drugs, such as cefmetazole, which can lead to elevated protein levels and black stools (4)
  • Perforation of the gastric tract due to the formation or ingestion of foreign bodies, such as hair, or large quantities of plant fibers, which leads to bleeding and anemia (5)
  • Hemolymphangiomas, or rare benign tumors that can affect different parts of the body and may cause bleeding and anemia (6)

What are the other possible effects of the red wine pigments?

Other possible effects of the red wine pigments are (3,7):

Red wine anthocyanins have anti-thrombotic effect and help prevent heart diseases

Red wine pigments possess strong anticancer effect, as demonstrated in several studies on esophagus, colon, breast, liver and prostate cancers

Red wine pigments have positive effects against diabetes, as they can improve the secretion of insulin

Anthocyanin pigments are important nutraceuticals in maintaining good vision and eye health

The ingestion of red wine pigments can help reduce body weight as well as decrease white and brown adipose tissue

Anthocyanins in red wine and grape, as in other fruits, can improve relaxation and help treat sleep disorders 


In this short article, we provided an answer to the question “can red wine cause black stools?” and the reason behind this.

  1. Ullman, Julius. The Clinical Importance of the Examination of Feces. Buffalo Med J, 1896, 36, 89.  
  2. Fitzgerald, Faith T., and Lawrence M. Tierney Jr. The bedside Sherlock Holmes. Western J Med, 1982, 137, 169.  
  3. Khoo, Hock Eng, et al. Anthocyanidins and anthocyanins: Colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food nutr res, 2017, 61, 1361779.  
  4. Haba, Yuichiro, et al. Hypoprothrombinemia During Cefmetazole Treatment: A Case Report. Am J Case Rep, 2022, 23, e936712-1.
  5. Al-Skaini, Mohamed S., and Mohamed I. Seleem. A rare cause of acute bowel obstruction. Saudi med j, 2000, 21, 585-586.
  6. Antonino, Antonio, et al. A very rare case of duodenal hemolymphangioma presenting with iron deficiency anemia. Int J Surgery Case Rep, 2014, 5, 118-121.
  7. Lin, Hsiao-Han, et al. Effect of kiwifruit consumption on sleep quality in adults with sleep problems. Asia Pacific j clin nutr, 2011, 20, 169-174.

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