Occasionally, stool may be flat, squarish, or stringy. These changes are often the result of diet. However, irritable bowel syndrome, chronic constipation, and other conditions may cause long-term changes in stool shape.

Poop should generally resemble the place from which it comes: the intestines. It is usually slightly rounded, like a sausage, and smooth, with some cracks on the surface.

It can be concerning if stools are suddenly not “normal.” Most of the time, however, a change in appearance is short-lived and nothing to worry about.

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Temporary changes to the shape or color of stool are common and not necessarily a sign of illness.

Sometimes, they stem from the person’s diet. For example, foods containing colorings can change the color of poop. An excess of fatty foods can lead to oily or greasy poop, and eating too little fiber can likewise give stool an unusual appearance.

If the changes only last for one or two bowel movements, or even a couple of days, they are likely no cause for concern.

However, if changes in stool shape or color last longer or accompany other symptoms, the cause may be an underlying condition that requires medical attention.

Learn more about different types of poop here.

While changes in the color or appearance of stool often stem from the diet and are temporary, some underlying health issues can cause more lasting changes.

Below, we describe some conditions that may cause flat poop:

Irritable bowel syndrome

Irritable bowel syndrome (IBS) refers to a group of gastrointestinal symptoms that occur without any visible signs of damage or disease in the digestive system.

Symptoms include:

Treatment may include:

Learn more about the signs of IBS here.

Constipation

Constipation involves having fewer bowel movements than usual or having hard stool that is difficult to pass.

Symptoms include:

Treatment may include:

Find home remedies for constipation here.

Diarrhea

Diarrhea is the passage of loose or watery stools several times a day. It may also involve pain or discomfort.

Symptoms include:

Treatment may involve:

  • taking over-the-counter diarrhea medication
  • treating the underlying cause
  • replacing lost fluids and electrolytes

Learn how to stop diarrhea fast here.

Colorectal cancer

Changes in the shape of stool can be one sign of colon or rectal cancer. If a tumor grows in either area, it can change the shape of the bowel and cause stool to be flat or thin and pencil-like.

Symptoms include:

Treatment may include:

  • surgery to remove the cancerous cells
  • radiofrequency ablation, which involves killing these cells with a probe containing tiny electrodes
  • cryosurgery, which freezes and destroys the abnormal tissue
  • chemotherapy, which involves stopping cancer’s growth with drugs
  • radiation therapy, which involves using high energy X-rays, for example, to kill cancerous cells or keep them from growing
  • targeted therapy, which involves attacking cancerous cells, without harming regular cells, using drugs or other substances
  • immunotherapy, which involves using the immune system to fight the cancer

It is important to remember that the earlier a doctor diagnoses cancer, the better the likelihood of successful treatment.

Learn more about colorectal cancer here.

Other potential causes

Anything that may cause the colon or rectum to narrow may also cause flat poop. These issues include:

The best approach depends on the cause of the issue. Some home care techniques involve:

Fiber

If constipation causes flat stool, eating more fiber-rich foods can help.

Foods with high fiber content include whole grains and many fruits and vegetables. Leave the skins on, when possible.

Learn about high fiber foods here.

Water

Drinking lots of water can ease the passage of stool, making it less likely to be flat.

Learn about the symptoms of dehydration here.

Exercise

Some types of physical activity may have a positive impact on gastrointestinal problems.

Activities such as walking, yoga, aerobic exercise, and tai chi may help improve physical and mental health-related symptoms of IBS, according to research from 2019.

Low FODMAP diet

FODMAP stands for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.” These are short-chain carbohydrates that can be poorly absorbed by the small intestine and can cause gastrointestinal symptoms.

Evidence supports the use of a low FODMAP diet in the treatment of IBS.

Learn more about the low FODMAP diet here.

Flat poop is rarely a cause for concern. However, a person should seek medical advice if any of the following symptoms occur:

  • blood in stool
  • dark stool
  • pus or mucus in stool
  • high fever
  • abdominal pain or cramping
  • sudden, prolonged constipation
  • pooping more or less often than usual
  • drastic changes in the consistency of stool

Overall, if thin or flat stool occurs for more than 3 days, even without any of the above symptoms, a person should consider contacting a doctor.

Here are some questions people ask about flat poop.

Is flat poop normal?

Flat poop is not usually a cause for concern. However, people should speak with a doctor if they have blood in their stool or persistent changes in bowel habits for no clear reason.

What can flat poop mean?

Flat poop can be a sign of constipation, diarrhea, irritable bowel syndrome, an enlarged prostate, or colorectal cancer. Stool can also change in color and consistency according to the diet.

Bowel movements naturally vary from day to day, and these temporary changes are usually nothing to worry about.

However, prolonged changes can indicate an underlying health issue. If flat poop occurs for more than 3 days, seek medical advice. It may be wise to do so earlier if there are other symptoms.