Green Bowel Movement and Green Diarrhea – What Are the Causes?

Varying shades of brown is accepted as the normal stool color but sometimes it may be other colors. Most of these other hues are considered as abnormal. One of these abnormal colors ia green tinge to overtly green color of the bowel movement. It has to be investigated as this can be a sign of various diseases. The condition is even more serious if there is diarrhea that is green.

Most of the time green bowel movement and green diarrhea are thought to be due to bile. This is the substance that is produced by the liver and stored in the gallbladder. Bile is naturally a greenish color and released into the small intestine during the digestion of food. However, bile is reabsorbed and also processed by colonic bacteria which yields a yellow to brown color that gives stool its natural color.


Causes of a Green Bowel Movement

Green bowel movement that is of normal consistency and not overly frequent like in diarrhea is mainly due to strong dyes or colorants staining the stool a green color. This may arise with certain foods, beverages, medication and supplements. Sometimes these substances are not green in color but with digestion and interaction with other substances in the bowel, these substances may make the stool appear green in color.


Green bowel movement may be normal for a person that ingests a lot of:

  • Green leafy vegetables like broccoli, lettuce, spinach, cabbage
  • Black licorice
  • Baby formula – vegetable mashes
  • Artificial colors, commonly added to ice creams, soda, fruit juices, or other drinks, morning cereals, milk products, sweets, etc.
  • Iron-rich foods like enriched breakfast cereals, red meat, spinach, beans, etc.

Dark green color may persist for up to five days after ingesting above mentioned foods. Supplements or artificial colors may give bright green color to the stool.

In infants, stool is green in the first few days after birth. This is normal. It may also occur later in infancy due to breastfeeding. Some baby formulas may also cause a green color f infant stool. Children on a clear-liquid “starvation diet” during illness may have green watery stools since bile is the only substance that is passing through the gut and out of the bowels.

Medications and Supplements

Certain medication and supplements, that are taken orally, may cause green bowel movement for several different reasons. The following drugs and supplements are more likely to cause green bowel movement:

  • Iron supplements
  • Laxatives – due to shortened bowel transit time (movement through the gut).
  • Algae
  • Chlorophyll
  • Children syrups often contain sweeteners fructose or sorbitol that both can speed up peristalsis what may result in green bowel movements.
  • Vitamins /mineral supplements, or eventually any other medication or supplement taken by mouth, if it is artificially colored, or if it contains fructose or sorbitol, that may speed up movement through the bowels.

Causes of Green Diarrhea

Sometimes an abnormally green color of the stool is also associated with diarrhea. Therefore the diarrheal stool apears green in color. In these cases the greenish hue may be due to the unprocessed bile or due to other causes that can taint the stool green while causing diarrhea simultaneously. For example, a green colored alcoholic beverage like sambuca can cause diarrhea when consumed in excess while tainting the stool with its strong green color.

Decreased Bowel Transit Time

Green bile, after excretion from the liver into duodenum, slowly changes to yellow, and then to brown color due to chemical changes performed by normal intestinal bacteria and enzymes. When the bowel content flows through the intestine fast, original bile color does not change, resulting in green or yellow stool. Causes of decreased bowel transit time include:

  • Diarrhea –  there are several causes of loose bowel movements, including food poisoning (giardia and salmonella infection often result in green diarrhea), rotavirus infection, food allergies, lactose intolerance, fructose malabsorption, celiac disease, Crohn’s disease, ulcerative colitis, and so on.
  • GERD (Gastroesophageal Reflux Disease) is where there is reverse flow of stomach acid and in some instances there may be associated diarrhea which can be significantly stained with bile.
  • Thyrotoxicosis – elevated levels of hormone thyroxine in the blood, usually due to autoimmune thyroid disorder (Grave’s disease)
  • Impaired gut innervation, common in diabetes when a condition known as diabetic neuropathy occurs. This alters bowel motility.

Impaired Bile Re-absorption in the Small Intestine

As bile passed down the gut, it is processed by the digestive system. Bile salts that are in the bile and largely responsible for its green color is reabsorbed to some extent. It is then processed again by the body. Bile salts are absorbed into blood mainly from last part of small intestine (terminal ileum). Causes of impaired bile re-absorption includes:

  • Inflammation of the small intestine, mainly due to Crohn’s disease
  • Surgical removal of the terminal ileum

Some of these bile salts are then secreted again in to the bowel through the bile or processed by the kidney and expelled with urine.

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What to Do for Green Bowel Movements?

Green bowel movements due to ingested food or medication/supplement are normal, and may not require any medical intervention. The stool will return toa  normal color once the causative substance is flushed out of the digestive tract. However, medication and supplements should not be stopped until a doctor or pharmacist advises so. Green bowel movement is not always serious in these cases but should nevertheless be investigated if it is persistent.

Fatty Stool Diarrhea

In all other cases, especially if symptoms like fever, diarrhea, constipation, weight loss, or general malaise are present, then it needs to be investigated by a medical professional. Sometimes this greenish stool can be due to a serious underlying disorder. It is important to bear in mind that greenish bowel movement is just a symptom some underlying condition or temporary disturbance. A stool sample may have to be collected and sent to a laboratory for analysis.

Last updated on September 3, 2018.

About Jan Modric (209 Articles)
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