Diverticulitis Stool: All You Need to know (Shape, Colors, mucus, & More).

Our content is not intended nor recommended as a substitute for medical advice by your doctor. Use for informational purposes only.

If you’ve been diagnosed with diverticular disease or diverticulitis, You will be more concerned about the shape and the color of your stool.

The stool is often affected in different ways in acute diverticulitis and diverticular disease.

Before we discuss the stool changes with diverticular disease and diverticulitis, You should first know some basic concepts about this condition.

Diverticulosis, diverticular disease, and acute diverticulitis are different from each other.

  • Diverticulosis: means the presence of diverticula in the colon (more common in the left-sided colon (especially the sigmoid colon in the lower left abdomen). Diverticulosis is asymptomatic and its incidence increases with age.
  • Diverticular disease: refers to symptoms associated with diverticulosis.
  • Diverticulitis: acute inflammation of the diverticula often presents with severe symptoms such as fever, severe abdominal pain, and changes in bowel habits.
  • Diverticular bleeding: bleeding from the diverticular (often painless bleeding that occurs with or without diverticular inflammation.

1. Diverticulitis stool shape.

The normal stool often takes the shape of your colon or intestine (being round and lumpy in nature). The diverticular disease (presence of diverticula without inflammation) often doesn’t affect the stool shape.

However, acute diverticulitis may alter the shape and consistency of your stool by different mechanisms:

  • Alternation of the colon contractions and motility, making the stool more soft or hard.
  • Narrowing of the colon lumen (due to inflammation and swelling of the colon walls or due to formation of a stricture).
  • Compression of the colon wall by a diverticular abscess or inflammatory mass.
  • Alternation of the stool content (more blood or mucus in the stool).

A. Diverticulitis thin (narrow) stool.

Acute diverticulitis may cause thin (narrow) or pencil-shaped stools. The inflamed swollen colon wall often causes narrowing of the colon lumen leading to the thin pencil-shaped stool.

Thin or narrow stool doesn’t always mean diverticulitis flare-up. They may occur due to a variety of other causes such as:

  • Concomitant irritable bowel syndrome.
  • Food intolerances or indigestion.
  • Too much fiber or fiber supplements with diverticular disease.
  • Any other conditions that cause loose stool or diarrhea such as medications, or acute stress.
  • Rarely, It can be a result of a more serious condition (colorectal cancer).

So, Having occasional thin stool shouldn’t be a worrisome sign unless you have symptoms typical for acute diverticulitis which include:

  • Severe abdominal pain (commonly in the left lower abdomen, but it can occur anywhere in your abdomen.
  • Fever.
  • Nausea, loss of appetite, or vomiting.
  • Tender abdomen on touch.
  • Sometimes, a sense of mass (at the left lower abdomen).
  • Constipation or diarrhea.
  • Mucus or blood in the stool.

B. Diverticulitis flat stools.

Flat stool may refer to a soft, thin, and loose stool. It is due to the loss of the standard bulky and rounded shape of the stool.

Flat stool may occur with acute diverticulitis due to changes in bowel habits (loose stool or diarrhea). It is also can be a sign of partial obstruction of the colon.

However, you should remember that stool changes alone are not indicative of acute diverticulitis. You must have other symptoms and signs of acute diverticulitis (mentioned above).

2. Diverticulitis stool colors.

Normally, all shades of brown are normal for the stool of healthy people. The possible color changes with diverticulosis and acute diverticulitis include.

A. Yellow stool:

Yellow stool with diverticulitis can arise from simple causes such as high-fat and yellowish food. Also, yellow stool may develop due to speeding up of gastric contents (with diarrhea or loose stool).

Diarrhea that causes yellow stool is common with acute diverticulitis (23% of patients with acute diverticulitis have diarrhea). Loose stools are even more common.

Yellow stool without the symptoms of acute diverticulitis (pain, fever, tender abdomen, etc.) is not suggestive of an acute attack.

B. Reddish blood or reddish spots in the stool.

Painless bleeding from the non-inflamed diverticula is common. Passage of frank red blood or bloody stool is an indication of diverticular bleeding.

Significant amounts of blood in the stool with the diverticular disease require you to seek emergency medical help.

Reddish spots in the stool may also be a sign of slight bleeding. Call your doctor for further assistance.

C. Black or blackish spots in the stool.

The very dark brown stool can be a normal variant, especially in people with constipation or after ingestion of blackish foods or supplements.

However, rarely, diverticulitis can affect the right side of the colon causing black stool or blackish spots in a brown stool.

Black stool is a sign of bleeding, you should consult your doctor if you have tarry black or fishy-smelling stools.

We discussed the causes of black stool in the below article with more details:

D. Green stool with acute diverticulitis.

Green stool is rare with acute diverticulitis. It may occur due to severe attacks of diarrhea. If you have green stool without diarrhea, It may be due to the food you eat.

Green leafy vegetables are the most common cause of green stool in people with diverticular disease. It is not a cause of concern as long as you don’t have diarrhea or other symptoms of acute diverticulitis.

3. Mucus in the stool with diverticulitis.

Diverticulitis may cause severe inflammation of the colon (commonly the left descending colon and the sigmoid colon).

Inflammation of the colon with acute diverticulitis may cause increased mucus in the stool with or without changes in your bowel habits.

Mucus in stool with severe abdominal pain, fever, and tenderness over the left side of the abdomen is suggestive of an attack of acute diverticulitis.

However, you should consider other causes of mucus in the stool such as:

  • Dehydration.
  • Constipation.
  • Common diseases such as irritable bowel syndrome, acute gastroenteritis, and others.

When to worry about stool changes with diverticular disease.

Most of the stool changes with diverticulitis are not specific to diverticular disease and cannot be used as a clue for acute diverticulitis.

Consider acute diverticulitis when you experience:

  • Bloody or blackish stool or frank bleeding per rectum.
  • Severe diarrhea.
  • Recent onset abdominal pain (particularly left lower abdominal pain).
  • A sense of tender mass in the left lower abdomen.
  • Fever.
  • Recent onset nausea, anorexia, or vomiting.
  • Signs of severe bleeding such as shortness of breath, fast heartbeats, dizziness, confusion, extreme thirst, etc.