Key takeaways

  • 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.
  • People can take steps at home to regulate their bowel consistency and frequency. Home remedies include drinking more water, eating more fiber, and exercising regularly.
  • If bowel changes persist for longer than a few days, it is a good idea to speak with a healthcare professional to identify the underlying cause.

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.

This article explains what can cause flat poop, how to fix it at home, and when to speak with a doctor.

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Temporary changes to the shape or color of stool are 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.

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 are some conditions that may cause flat poop:

Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a group of gastrointestinal symptoms that occur without any structural damage to the digestive system.

Treatment may include dietary changes, such as eating more fiber or switching to the low FODMAP diet.

Constipation

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

Symptoms include:

Diarrhea

Diarrhea is the passage of loose or watery stools three or more times a day.

Symptoms include:

Treatment may involve over-the-counter diarrhea medication and treating the underlying cause. It is also important to replace lost fluids and electrolytes.

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 for more than a few days.

Other 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.

Other potential causes

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

The best approach to manage flat poop 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.

Water

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

Exercise

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

A 2024 review suggests that exercise may help improve IBS symptoms by improving the range of bacteria in a person’s gut and relieving stress and anxiety, which could worsen symptoms.

Low FODMAP diet

FODMAP stands for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols.” The small intestine may have difficulty absorbing these short-chain carbohydrates, leading to gastrointestinal symptoms.

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

Flat poop is not always 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.

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.

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.

Anxiety can lead to changes in bowel habits, such as constipation or increased IBS symptoms, both of which can cause flat stools. If bowel changes persist, it is a good idea to speak with a healthcare professional.

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.