The Connection Between IBS and Other Bowel Diseases

Reviewed by: HU Medical Review Board | Last reviewed December 2022 | Last updated: January 2023

Symptoms of irritable bowel syndrome (IBS) are often mistaken as symptoms of other bowel diseases. Some of these bowel diseases are much more serious than IBS. It is important to get an accurate diagnosis since a misdiagnosis can delay getting the right treatment.

Figuring out the correct disease versus others with similar symptoms is called making a differential diagnosis. This involves several tests to rule out certain conditions.1

Continue reading to learn which bowel diseases often get confused with IBS.

Bile acid malabsorption (BAM)

Bile acid malabsorption (BAM) is common yet under-recognized. It causes watery diarrhea and an urgent need to use the bathroom. People who have IBS with diarrhea (IBS-D) often have BAM.2

The liver produces bile acids. A small amount of bile acid moves through the colon and passes from the body in the form of stool.2

With BAM, too much bile acid reaches the colon. This causes the colon to contract more than usual and speeds up the movement of stool. This leads to stomach pain, bloating, diarrhea, and the urgent need to use the bathroom.2

Inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD) is a complex disease that causes inflammation in the digestive tract. Crohn’s disease and ulcerative colitis (UC) are 2 types of IBD. While IBS and IBD have many similar symptoms, they are 2 distinct digestive disorders.3

IBD symptoms can include:3

  • Stomach pain and severe cramping
  • Bloating
  • Diarrhea that lasts several weeks and does not go away
  • Blood in your stool or on toilet paper
  • Urgent bowel movements
  • Nausea and vomiting
  • Loss of appetite
  • Weight loss
  • Fatigue

A big difference between IBS and IBD is that IBD can cause damage to the intestines. IBS does not.3

Colorectal cancer

Colorectal cancer starts as a growth (polyp) on the inner wall of the colon or rectum, which are parts of the large intestine. Symptoms of colorectal cancer are similar to IBS symptoms – constipation, diarrhea, and stomach pain – but IBS does not cause colorectal cancer.4

Colorectal cancer can come with other symptoms that are different from IBS, including:4

  • Rectal bleeding
  • Blood in the stool
  • Unexplained feeling of fullness
  • Sudden, unexplained weight loss

Small intestinal bacterial overgrowth (SIBO)

Small intestinal bacterial overgrowth (SIBO) occurs when the bacteria in your gut is out of balance. The intestines are home to millions of microorganisms. These bacteria help keep your gut healthy. But if there is an imbalance of bacteria or too much of the wrong kind of bacteria, it can cause symptoms that are similar to IBS, like gas and diarrhea.5

SIBO leads to poor digestion and poor absorption of food. When you do not absorb food well, you are not getting the vitamins and nutrients your body needs.5

SIBO and IBS can coexist. In fact, about 80 percent of people with IBS also have SIBO.5

Diverticulitis

Diverticula are small bulges that form in the large intestine. These outward bulges can get inflamed or infected. This causes a condition called diverticulitis.6

The most common symptoms of diverticulitis are:6

  • Pain on the left side of the stomach
  • Fever
  • Tender and inflamed mass in the left lower area of the stomach

People with diverticulitis may have IBS symptoms such as stomach pain, constipation, or diarrhea. A 2020 study found that people with IBS are at an increased risk of developing diverticulitis.6

Chronic pancreatitis

The pancreas produces enzymes that play a role in digestion. In chronic pancreatitis, the pancreas is inflamed. Over time, it becomes damaged and cannot digest food as it should.7

Most people with chronic pancreatitis have upper stomach pain. Pain can come on fast and can be severe. Pain can also come and go. This makes it hard to diagnose. Other symptoms of chronic pancreatitis may include:7,8

  • Nausea and vomiting
  • Diarrhea
  • Weight loss
  • Greasy, floating stools (steatorrhea)

While there is some overlap of symptoms, IBS and chronic pancreatitis are 2 different conditions. The following health problems can cause chronic pancreatitis:8

  • Heavy alcohol use
  • Cystic fibrosis
  • Autoimmune conditions
  • A blockage in the pancreatic duct or common bile duct
  • Hereditary pancreatitis
  • Carcinoid syndrome

    Carcinoid syndrome is caused by carcinoid tumors. These tumors are a rare type of cancer that produce chemicals in the bloodstream. They can develop in the digestive tract. The most common symptoms of carcinoid syndrome include:9

    • Flushing of the face
    • Stomach pain
    • Diarrhea

    Thyroid disease

    Microbes in the gut affect the body’s hormone levels. Any change in the gut microbiome could lead to thyroid disorders. Thyroid disorders include Graves’ disease and Hashimoto’s thyroiditis (HT).10

    Thyroid diseases can cause some digestive symptoms. But so far, there is no evidence that IBS causes thyroid diseases or that thyroid diseases cause IBS.10

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