Finding blood in your stool can be startling and even frightening. Blood can show up in your stool if you have any bleeding in the esophagus, stomach or intestines, and although this symptom may not reflect a serious condition, blood in the stool always needs to be evaluated by your doctor. While food is usually not the cause, foodborne illness, certain food allergies or celiac disease may lead to blood in the stool. In addition, certain diet patterns may increase the risk of conditions that cause gastrointestinal bleeding. Finally, some foods can change the color of the stool when blood isn’t really present, or otherwise give the false appearance of blood in the stool.
If you eat food that is contaminated with certain strains of bacteria, the resulting infection might cause bloody diarrhea. Certain organisms found in the feces of animals or infected humans can contaminate water, milk or other foods, and consuming undercooked or raw meat, unpasteurized milk or juice, or contaminated produce can lead to symptoms which include bloody diarrhea. Examples of bacteria that can cause this symptom include Campylobacter jejuni, certain strains of Escherichia coli (E.coli) and shigella. Another bacteria that can cause bloody diarrhea is Vibrio parahaemolyticus, which may be found in raw or undercooked seafood.
Immune Response to Foods
Food allergies are another cause of blood in the stool. According to a May-June 2015 review published in “Allergy and Asthma Proceedings,” bloody stools may be caused by food protein-induced inflammation of the intestinal tract. This is most often seen in infants and is usually linked to cow’s milk and soy formula, but a breastfed infant can also react to food proteins consumed by the mother. Children usually grow out of these allergies by age 3. If you have celiac disease, eating foods with gluten can lead to a variety of symptoms including inflammation of the small intestine and diarrhea -- and blood in the stool if symptoms are severe. The only treatment for this is to avoid gluten, which is found mainly in wheat, barley and rye.
Hemorrhoids, often noticed by bright red blood on the toilet tissue, is a common cause of blood in the stool. The straining and hard stools caused by constipation, which is linked to a low fiber diet, can lead to hemorrhoids, and this condition can be relieved by a diet high enough in fiber to promote soft, regular bowel movements. Another disease that can be averted by a high fiber diet is diverticulosis, a condition in which small, bulging pockets develop in the intestines. When these become infected and inflamed, intestinal bleeding can occur if the diarrhea and inflammation is severe. Long-term excessive alcohol intake can also lead to health complications which can cause bleeding in the esophagus, and this blood will also show up in your stool.
Certain foods can make it look like your stool contains blood, when it actually does not. Deep red or purple foods, such as beets, watermelon, blueberries or tomatoes, can be change the color of your stool, as can large amounts of red or purple candy or other foods with red food coloring. Some medications, including iron supplements, can also lead to the appearance of blood in your stool, while no blood is actually present.
Warnings and Precautions
Blood in the stool may show up as bright red blood coating the stool, or as a black or burgundy colored stool. While certain foods may cause blood in the stool, there are other more common causes of this symptom. The presence of blood may also be a sign of cancer, inflamed colon or other serious disorders that require medical treatment. If you notice any blood or color changes in your stool, contact your doctor. Seek immediate medical attention if you have sudden or large amounts of bleeding, or if you become weak, dizzy, faint or short of breath.
Reviewed by: Kay Peck, MPH, RD