Loose Stool – Types and Causes of Loose Bowel Movements

What is loose stool?

Most of us refer to any frequent or watery stool as loose stool. The term can be inaccurate at times when the bowel movement is frequent but the stool is of a normal consistency, or where the bowel habit is normal but the consistency of the stool is more watery than usual. Similarly the term loose stool is also used to describe diarrhea, which specifically refers to having a bowel movement more than three times in a day. Irrespective of the exact inference, the term loose stool denotes some abnormality in bowel habit and stool consistency that leans towards diarrhea rather than constipation.

Type of Stool

The consistency and shape of stool is a good indicator of bowel health as is the composition of fecess. The Bristol Stool Chart is a useful way to identify abnormalities in stool consistency in particular. It outlines seven different types of stool with hard stool characteristic of constipation at one end (types 1 to 3) and watery or loose stool at the other end (types 5 to 7). A normal stool is considered to be soft, smooth and elongated like a sausage (type 4).

Bristol Stool Chart

Why is stool loose?

Stool can be classified as loose when its normal formation is disrupted. Normally fluid chyme (the digested contents from the smallintestine) enters the colon and water is drawn out of it until it forms a soft solid mush that is known as stool. With loose stool, the water content is much higher and therefore the stool cannot form a firm and somewhat solid mass. This disruption in water reabsorption arises when the colon is diseased or stool moves too fast through the colon.

Furthermore, a lack of fiber prevents the stool frombinding effectively and absorbing sufficient water to result in well-formed stool. A change in the composition of stool can lead to more water being retained within the stool than reabsorbed due to a difference in osmotic concentration. Sometimes multiple factors that affects the consistency of stool may be present thereby leading to very loose stool or completely watery stool with almost no remnants of solid matter.

Causes of Loose Stool

The causes of loose stool are largely the same as diarrhea. Firstly loose stool is another term for diarrhea that is used in everyday communication. Secondly the same processes that lead to diarrheal stool will also contribute to loose stool.


This is one of the most common causes of loose stool. It is usually acute meaning that it is short-lived in most cases. Gastroenteritis is mainly due to viral infections but can also arise when bacteria and other parasites enter the gut. Sometimes toxins from these microbes may be the problem and can contaminate food or water.

Foods and Drinks

Sometimes a change in diet can temporarily upset the normal bowel habit and stool consistency. This is often seen with spicy and oily foods but can apply to just about any food or beverage that is not a regular part of the diet. Alcohol and large amounts of caffeine can also be a problem and lead to bowel irritation which may result in loose stool.


A lack of dietary fiber may also cause loose stool. This happens when the fiber content in the diet is low for long periods of time. People who tend to eat too much of processed foods and too little fiber-rich foods like fresh fruit and raw vegetables may find that the stool is loose compared to a normal consistency.


There are times where abnormalities in bowel habit may lead to loose stool although there is no underlying disease. This may be seen with irritable bowel syndrome (IBS) which is classified as a functional bowel disorder. In IBS with diarrhea, the problem appears to lie with faster bowel motility and normal firm but soft stool cannot form properly since stool moves too fast through the bowels.


One non-infectious inflammatory condition where loose stool and diarrhea may be seen is inflammatory bowel disease (IBD). This is an autoimmune condition where the immune system attacks the bowel wall and causes inflammation. As a result digestion and absorption is impaired and loose stool is one of the symptoms, along with blood and mucus in the stools particularly during flareups.

Food Intolerance

With food intolerances, the body may be unable to digest or absorb certain nutrients in food. As a result these undigested nutrients draws out more water into the bowels, irritates the bowels and may change the bowel bacteria. The most common type is lactose intolerance where the body lacks the enzyme lactase to digest milk sugars (lactose).

Celiac Disease

Celiac disease is a condition where the bowel becomes inflamed due to the presence of wheat and specifically the protein in wheat known as gluten. When this protein comes in contact with the bowel, it triggers an immune reaction similar to an allergy. This causes the bowel wall to become inflamed. Both digestion and absorption of nutrients are then impaired.

How to diagnose loose stool?

Ideally loose stool should be investigated and the underlying cause needs to be diagnosed by a medical professional. This may require further tests like a stool analysis. However, it is also important to take note of dietary and lifestyle factors that may be contributing to loose stool. The following measures may help with diagnosis:

  • Keep a food diary. Take note of foods that may trigger loose stool. The change in stool consistency may only arise 24 to 48 hours after eating the trigger food.
  • Try an elimination diet. Remove possible trigger foods from the diet and gradually reintroduce these foods. If loose stool starts up again then the food in question is probably the trigger.
  • Eat more fiber. Increasing dietary fiber may help to form stool that is firm but soft. This is particularly useful for people who eat a large amount of refined food and too little fruits and vegetables. Fiber supplements may also help.
  • Take probiotics. The normal intestinal flora (“good” bowel bacteria) play an important role in bowel health and stool composition. Probiotics can be taken in the form of capsules or in certain foods like live culture yogurt.

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