What Your Stool Is Telling You

By Robynne K. Chutkan, MD, FASGE Assistant Professor of Medicine, Georgetown University Hospital Founder and Medical Director, Digestive Center for Women

Posted on | By Dr. Robynne Chutkan
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Warning Signs in Your Toilet, Pt 1 (5:12)

When trying to figure out the significance of a symptom you may be having, it's helpful to think in terms of what's the most likely diagnosis and what's the most lethal. Hopefully they are not the same. For example, the most likely cause of red blood in the stool is hemorrhoids, but the most lethal is colon cancer.

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Taking a close look at your stool can tell you a lot about what's going on in your intestines and can lead you to make the right changes to improve your digestive and overall health. If you know what to look for, it's like reading tea leaves! I tell my patients that if they pay close attention to what's going on in the bowl, they might not need my services.

Here's a guide to some of the most likely – and most lethal – conditions that can lead to changes in the shape, size, smell and shade of your stool.

Shape

Insufficient fiber in the diet, diverticulosis, bowel spasm or excessive straining are common causes of a change in stool shape. Diverticulosis causes pothole-like craters in the lining of the colon, as well as a narrowing of the internal diameter of the colon due to wall thickening. The result is narrow, pellet-like stools that often fall apart in the bowl and can be difficult to expel. Other associated symptoms of diverticulosis include a dull ache in the lower abdomen, a feeling of incomplete evacuation even though you may be having multiple bowel movements, and lots of gas and bloating. Endometriosis, uterine fibroids, masses in the abdomen or tumors in other organs, like the ovaries or bladder, can cause thin stools due to external compression of the colon. Colon cancer definitely needs to be excluded by a colonoscopy in anyone experiencing new onset of pencil-thin stools, which can occur as a tumor gets larger and grows inward, reducing the colonic diameter.

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Size

Size matters. Small, hard stools are typical in people eating a low-fiber Western diet, and are associated with a higher risk for ultimately developing diverticulosis and colon cancer. Constipation is often associated with small, difficult-to-pass stools, and people suffering from constipation-predominant irritable bowel syndrome (IBS) are particularly prone to having small stools. A high-fiber diet or regular use of a bulking agent like psyllium husk will lead to larger, softer stools in most people, making defecation easier. Even though a fiber-deficient diet is the most likely culprit, colon cancer is again on the list as most lethal.

Smell

The odor of your stool is highly dependent on a number of factors, including how long it's been sitting in your colon, your diet, medications you may be taking and, in some cases, the presence of infection. Bacterial imbalance (dysbiosis) in the GI tract and undigested fat can also lead to a change in odor.

The most common cause of smelly stool is bacterial fermentation of the food in your intestines that produces foul-smelling sulfide compounds. Antibiotics can also change the smell of stool and give it a medicinal odor. More lethal causes of malodorous stool, and fortunately much less common, include inflammation of the pancreas (pancreatitis) and pancreatic cancer. Both these conditions can result in floating, foul-smelling stool with an oily sheen.

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Diseases that cause malabsorption of nutrients like Crohn's, celiac disease and cystic fibrosis can also lead to foul-smelling stool. Infection with parasites such as giardia lamblia can cause stool to have a very unpleasant odor.

New onset of diarrhea associated with a foul odor should prompt an evaluation for infection, whereas fat in the stool associated with a foul odor should raise concerns about malabsorption or pancreatic disorders. For most people, smelly stool is simply a byproduct of the beans they had for dinner the night before.

Shade

The color of stool can vary dramatically and can also be a clue as to whether various disease states are present.

Normal stool is brown due to its composition: bacteria, water, bile, bilirubin, broken-down red blood celIs and indigestible plant matter like cellulose, along with small amounts of protein and fat.

LEARN MORE: Use This Printable Poop Log

Red stool is most worrisome as it indicates bleeding in the lower GI tract from conditions like hemorrhoids or diverticulosis, or more serious conditions like rectal cancer. Red stool can also be caused by ingesting red food coloring or beets. While it should always be reported, it's not always an ominous sign.

Green stool can occur with rapid transit through the intestines where bile doesn't have a chance to be broken down to its final brown color. Green can also be a sign of Crohn's disease, antibiotic use, ingestion of leafy greens or iron therapy.

Yellow stool can be the result of gallbladder dysfunction which causes improper handling of bile. Infection with giardia lamblia produces a characteristic yellow diarrhea. In addition to causing diarrhea, different types of infection in the GI tract, whether viral, bacterial or parasitic, may cause changes in stool color.

White stool can be a sign of fat malabsorption, as with pancreatitis and pancreatic cancer, but barium used for X-rays can also give the same appearance. Mucus in the stool can give it a whitish appearance and may be due to inflammation or benign conditions like IBS.

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Black stool should trigger a search for bleeding from the upper part of the GI tract (esophagus, stomach or small intestine), but can also be seen with iron therapy, heavy meat consumption, and bismuth-containing compounds.

Light-appearing clay-colored stools are characteristic of liver disease and decreased bile output, but can also be caused by antacids containing aluminum hydroxide. Vitamins and supplements commonly cause changes in urine color but may also change stool color. 

For Dr. Oz’s Poop Color Chart, click here.

Article written by Dr. Robynne Chutkan
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