Constipation and SIBO: What’s the Connection?
Constipation and SIBO are often discussed together — but they are not the same thing.
Many people with chronic constipation experience bloating, gas, and abdominal discomfort. Because these symptoms overlap with Small Intestinal Bacterial Overgrowth (SIBO), it’s common to assume SIBO is the cause. In reality, the relationship is more nuanced.
Constipation can increase the risk of SIBO, and SIBO can also worsen constipation. In many cases, constipation alone fully explains digestive symptoms — without any bacterial overgrowth present.
Understanding the difference matters, because treating the wrong problem often leads to frustration, symptom cycling, a waste of resources, and unnecessary protocols.
Can constipation cause SIBO?
Yes, chronic constipation can increase the risk of SIBO in some individuals.
When bowel movements are infrequent or incomplete, intestinal contents move more slowly through the digestive tract. This reduced motility creates an environment where bacteria can accumulate and move upwards into the small intestine rather than being cleared effectively.
Over time, this can contribute to:
Bacterial overgrowth > Increased gas production due to fermentation of carbohydrates > worsening bloating and discomfort
However, not everyone with constipation develops SIBO, and slow transit alone does not equal bacterial overgrowth.
Methane gas, motility, and constipation
SIBO manifests in different forms, each with its unique impact on bowel regularity. Hydrogen SIBO, Methane SIBO (now also referred to as Intestinal Methanogen Overgrowth, or IMO) and Hydrogen-Sulfide SIBO (H2S SIBO) constitute the SIBO spectrum.
Methane-dominant SIBO (IMO) is the main type commonly associated with constipation. Elevated methane gas levels is a byproduct of archaea (or methanogens) activity in the gut.
Methane gas has been shown to slow intestinal transit, which can:
Reduce stool frequency
Increase stool hardness
Make constipation more persistent and harder to treat
This creates a feedback loop:
Slow motility → more methane → slower motility
That said, methane is not the only cause of constipation, and its presence should always be interpreted in context rather than assumed.
Note: constipation can also be seen in cases of Hydrogen and Hydrogen Sulfide SIBO, although these occurrences are more rare.
Changes in the Gut Microbiome with SIBO
The overgrowth of bacteria in the small intestine disrupts the balance of the gut microbiome. This imbalance influences the digestion and absorption of nutrients, directly impacting bowel movements and paving the way for constipation. Restoring this microbial balance becomes pivotal in addressing both SIBO and its associated constipation.
SIBO ignites inflammatory responses within the gut, further complicating the environment. These inflammatory signals can disrupt intestinal motility, contributing to constipation. Understanding and addressing these inflammatory triggers to lower inflammation is an important step in managing both SIBO and its digestive repercussions.
When Symptoms Are Due to Constipation Alone
Many people can experience bloating, gas, abdominal pressure, and discomfort purely from constipation, without any overgrowth in the intestines.
When stool sits in the colon for too long, it can also ferment — producing gas — leading to abdominal distension and discomfort that mimics SIBO symptoms.
In these cases:
Breath tests may be negative or inconclusive
Antimicrobials provide little or temporary relief
Symptoms improve primarily when bowel regularity improves
Common causes of constipation without SIBO include:
Inadequate fibre intake (or poorly tolerated fibre)
Pelvic floor dysfunction
Poor gut-brain signalling
Chronic stress
Dehydration or electrolyte imbalance (ex: low potassium intake)
Low physical movement
Nervous system dysregulation
Hormonal influences (ex: progesterone, thyroid)
If constipation is not addressed directly, treating SIBO alone will not resolve symptoms, even if SIBO is present.
IBS-C vs SIBO
IBS-C (constipation-predominant IBS) and SIBO share many symptoms, including:
Bloating
Abdominal pain
Food sensitivity
Irregular bowel movements
However, IBS-C is a functional gut disorder, meaning symptoms arise from altered gut-brain signalling, motility, and sensitivity — not necessarily infection or overgrowth.
Many people with IBS-C also have SIBO. Some do not.
This is why symptom-based diagnosis alone is unreliable, and why testing should always be interpreted alongside clinical patterns.
Whether SIBO is present or not, constipation must be treated as a root issue, not a side symptom.
Diet Changes and Constipation
SIBO often prompts individuals to modify their diets as a coping mechanism.
Ever heard of Low FODMAP diet? Or the Carnivore diet?
Carbohydrate and fiber reduction, while temporarily providing relief from SIBO symptoms, can inadvertently contribute to constipation. These dietary adjustments, although at times beneficial for short-term SIBO management, necessitate a slow approach to reintroduction to ensure regular bowel movements.
Underlying Conditions linked to constipation
SIBO may be a constipation culprit, but it's often the consequence of deeper-rooted issues. Underlying conditions like yeast overgrowth and bacterial dysbiosis could be both the instigator of SIBO/SIFO and a direct cause of constipation. To truly address constipation linked to SIBO, a holistic approach that looks into these layers of root causes is essential.
If constipation has become a recurring theme in your gut health narrative, considering SIBO as a contributing factor could provide a pivotal piece to the puzzle for you.
If you are seeking relief, I have created a FREE Constipation Guide to help you get your poops back! Click on the button below to access the download page.