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Constipation and the Gut-Brain Axis


Written by: CDHF

Updated: December 6th, 2023

Constipation is something that we have all dealt with at some point in our lives. It is one of the most common gastrointestinal complaints that patients bring up with their healthcare professional. Constipation has an average prevalence of 16% worldwide, which varies across countries (Forootan, et. al., 2018). One in four Canadians struggle with constipation, contributing to approximately 1 million physician visits annually (Abdullah et al., 2015). 

What is constipation?

Constipation has been broadly defined in literature as the difficult passage of hard, dry stool or the infrequent passage of stool with typically fewer than three bowel movements per week (John Hopkins Medicine, n.d.). It may involve a feeling of incomplete emptying following a bowel movement (Gotfried, 2022). 

Bowel movements are highly variable and subject to influence by multiple factors including age, physiology, diet, and social and cultural influences (Gotfried, 2022).  A “normal” or “regular” schedule of bowel movements may be as many as 2-3 bowel movements per day or as few as 3 bowel movements per week. The question you need to ask is “how often do I poop?” to work out your baseline bowel movements (Gotfried, 2022). 

It is important to note that constipation is not a disease, but it may be a symptom of an underlying issue. Fortunately, it is usually a benign condition and not suggestive of something serious.

Signs and symptoms of constipation

You may experience one or more of the following symptoms:

Diagnosing Constipation

Constipation is usually diagnosed using the above-mentioned symptoms. Most of these symptoms form the basis of a diagnostic criteria known as “Rome IV Criteria”. According to it, functional constipation can be diagnosed if a person experiences at least two of the following symptoms over the past 6 months:

  1. Straining during more than ¼ (25%) of defecations
  2. Lumpy or hard stools (Bristol Stool Form Scale 1-2) more than ¼ (25%) of defecations
  3. Sensation of incomplete evacuation more than ¼ (25%) of defecations
  4. Sensation of anorectal obstruction/blockage more than ¼ (25%) of defecations
  5. Manual maneuvers to facilitate more than ¼ (25%) of defecations (e.g., digital evacuation, support of the pelvic floor)
  6. Fewer than three bowel movements per week
  7. Loose stools are rarely present without the use of laxatives
  8. Insufficient criteria for irritable bowel syndrome (The Rome Foundation, 2016)

What are the causes of constipation? 

Normally as food moves through the colon, water is absorbed, and stool is formed. If food moves too slowly through the colon, too much water will be absorbed, resulting in hard, dry stool.

Some of the most common causes include:

Stress and constipation

Simply put, it comes down to the “brain-gut axis”. In other words, your brain and gut are known to talk to each other. You may remember those stressful moments when you had “butterflies in your stomach” or made a decision by “going with your gut”. Research shows that the brain and the gut are intimately connected, sharing bi-directional communication which makes up the “brain-gut axis” (Harvard Health Publishing, 2019). 

The human brain is composed of approximately 86 billion neurons (nerve cells) (Voytek, 2013). The human gut is comprised of an extensive network of 200-600 million neurons (nerve cells) known as the enteric nervous system (ENS) (Furness et. al, 2014). One method of communication is the vagus nerve, a thick cable of neurons, which carries electrical signals, allowing for information sharing within milliseconds. In fact, 90% of the neurons in the vagus nerve carry information from the gut to the brain. Another means of communication is the gut microbiota, the trillions of microorganisms living in the human gut (Gerrie, 2020). These microbes along with the brain and gut release neurotransmitters (chemical signals) which influence each other and overall wellbeing. 

This “brain-gut axis” helps explain why stress may cause digestive problems.

Strategies to relieve constipation

Constipation can often be treated through dietary and lifestyle changes to relieve symptoms and help prevent constipation. These include:

Can medications help manage or prevent constipation?

Laxatives are a type of medication which may improve constipation and constipation-related symptoms. They are often used if diet and lifestyle changes are ineffective. They are available over the counter (OTC) and by prescription. They come as pills, powders, or suppositories. There are 4 main types of laxatives, each working in a slightly different way:

Lax-A Day® is a commonly used osmotic laxative, available OTC in powder form. The medicinal ingredient, polyethylene glycol, increases water content of stool and therefore making stool softer and easier to pass. .This product may not be right for you. Always read and follow the label. Lax-A Day®, is a registered trademarks owned by Norwell Consumer Healthcare Inc.

When should you see a doctor?

Sometimes there may be something more insidious going on. There is a phrase in gut medicine known as “alarm features” which are a set of specific features that may be associated with more serious health conditions. These include blood in stool, unintentional weight loss, sudden or progressive changes in bowel habits etc. If you experience any of these features, you should not hesitate to seek immediate medical help. Do not take any type of laxative for more than one week, unless recommended by a physician.


Abdullah, M. M., Gyles, C. L., Marinangeli, C. P., Carlberg, J. G., & Jones, P. J. (2015). Dietary fibre intakes and reduction in functional constipation rates among Canadian adults: a cost-of-illness analysis. Food & nutrition research, 59, 28646.

Cleveland Clinic. (2019, July 11). Constipation. Cleveland Clinic. Retrieved June 19, 2023, from

Common causes of constipation. (2021, February 15). Harvard Health.  Retrieved June 19, 2023, from

Constipation. (n.d.). John Hopkins Medicine. Retrieved June 24, 2023, from

Constipation: Practice Essentials, Background, Pathophysiology. (2020, March 30). EMedicine. Retrieved June 19, 2023, from

Forootan, M., Bagheri, N., & Darvishi, M. (2018). Chronic constipation: A review of literature. Medicine, 97(20), e10631.

Furness, J. B., Callaghan, B. P., Rivera, L. R., & Cho, H. J. (2014). The enteric nervous system and gastrointestinal innervation: integrated local and central control. Advances in experimental medicine and biology817, 39–71.

Gerrie, H. (2020, June 10). Our second brain: More than a gut feeling. UBC Neuroscience. Retrieved June 19, 2023, from

Gotfried, J. (2022). Constipation – Gastrointestinal Disorders. Merck Manuals Professional Edition. Retrieved June 19, 2023, from

Harvard Health Publishing. (2021, Feburary 15th). Common Causes of Constipation. Harvard Health. Retrieved June 19, 2023, from

Harvard Health Publishing. (2019, April 19). The gut-brain connection. Harvard Health. Retrieved June 19, 2023, from

Consipation. (n.d.). John Hopkins Medicine. Retrieved June 24, 2023, from

Polyethylene Glycol (Peg) 3350 – Oral. (2021). HealthLinkBC. Retrieved June 19, 2023, from

The Rome Foundation. (2016, January 16). Rome IV Criteria. Rome Foundation. Retrieved June 19, 2023, from

Voytek, B. (2013, May 20). Are There Really as Many Neurons in the Human Brain as Stars in the Milky Way? | Brain Metrics. Scitable by Nature Education. Retrieved June 19, 2023, from

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