The IBS/SIBO Weight Gain Relation

Grace Clark-Hibbs

May 17, 2021

In today’s society, weight management is hard enough. But throw in food allergies, intolerances or gut conditions such as IBS and SIBO, and it becomes d*** near impossible.

If you’ve ever wondered if there was a connection between your gas/bloating, sluggish gut, and constipation and your weight gain, you’re in the right place. I’m here to tell you that the IBS/SIBO weight gain relation is real and that poor digestion could be what’s holding you back from reaching your body’s optimal weight.

Quick Intro to IBS

IBS, or irritable bowel syndrome, is a functional gastrointestinal (GI) disorder – meaning the way the GI tract functions has been disrupted – and is defined as “abdominal pain or discomfort that occurs in association with altered bowel habits over a period of at least three months.” (1)

IBS is considered a chronic gut disorder that affects 7% to 21% of the population and can significantly impact a person’s quality of life. It is generally diagnosed after all other gut conditions have been ruled out and is characterized by a cluster of symptoms that can be caused by various circumstances. (2)

Some of these circumstances include: (2)

  • Changes to the gut microbiome (i.e. “gut bugs”)
  • Intestinal permeability
  • Gut immune function
  • Motility
  • Visceral sensitivity (i.e. sensitivity of the tissue and organs inside you abdomen)
  • Gut-brain axis via the vagus nerve

A variety of evidence-based treatment options exist for IBS, but effectiveness of each will vary person-to-person. These include, increasing soluble fiber intake, peppermint oil for abdominal pain, probiotics, hypnotherapy, and cognitive-behavioral therapy. (3)

Quick Intro to SIBO

Similar to IBS, SIBO (small intestine bacterial overgrowth) is a diverse condition that can present differently in different people. It is characterized by an abnormal amount of bacteria living in the upper portion of the small intestine. (4)

This imbalance is referred to as dysbiosis and will result in either slowed gut motility and constipation or faster than normal motility and diarrhea.

SIBO is often mis-categorized as the root cause of your uncomfortable gut symptoms, however there is generally an underlying issue (or issues) that is leading to changes in the gut microbiome.

These underlying issues can include: (5)

  • Low or no stomach acid
  • Past infection/trauma (including surgery)
  • Slow gut motility
  • Multiple courses of antibiotics
  • Hormone imbalances
  • Chronic stress

Treatment of SIBO is complex, highly individualized, and can sometimes take years. It involves addressing all underlying causes, alleviating symptoms and addressing any complications that may have come about. The tricky thing with SIBO treatment is that you have to get rid of every single “bad” bacteria otherwise it can quickly multiply and spread all over again. (5)

Can SIBO and IBS Exist Together?

The short answer is yes, however the evidence is weak and will require more research in order to fully understand the connection and pathology.

A study that reviewed 50 existing studies through July 2017, found that more than one-third of IBS patients also tested positive for SIBO. They also found that being a woman, being older in age, and having IBS-diarrhea had a greater association with SIBO.  (6)

However, another review from 2020 found that methane-positive breath tests (a test that indicates SIBO is present and is associated with slow motility and constipation) were more common in patients with IBS-C than in patients with IBS-D. This suggests that there is also a link between SIBO and IBS-constipation. (7)

That being said, a different study claims their data did not support SIBO playing a significant role in the symptoms of IBS even though they did find slight increases of small intestine bacteria in those with IBS. (8)

Long story short, there seems to be an increased prevalence of SIBO in patients with IBS, but it is still unknown which condition came first.

What Actually Causes IBS/SIBO Weight Gain?

The causes will be slightly different depending on whether you suffer predominantly from IBS or from SIBO. Let’s break it down by each condition.

IBS Weight Gain

IBS itself doesn’t usually directly cause weight gain. However, the condition is associated with changes in diet and lifestyle that can often contribute to weight gain. These changes include avoiding fiber-containing foods, such as fruits and vegetables, because they often lead to flare ups in the gut and uncomfortable symptoms.

It is not uncommon for someone with IBS to cut a significant number of foods out of their diet. People do this because they are afraid of how those foods will make them feel. This often leads to a limited diet that is high in refined grains and low in fresh produce.

IBS is also frequently linked with mental health conditions, such as depression, anxiety, and overall high stress levels. These conditions can lead to emotional eating patterns that lead to excess energy intake and eventually weight gain.

There are, however, two ways in which physiological changes associated with IBS are thought to contribute to weight gain. These changes are:

  • Abnormal gut hormone levels: The gut produces over fifty hormones that play important roles in the digestive process. Special cells that line the gut, called endocrine cells, are triggered to release different hormones at different stages of digestion. These hormones regulate many important functions such as sensation, motility, secretion, absorption, immune defense, appetite, and metabolism (including insulin sensitivity, glucose tolerance, and fat storage). (9, 10, 11)

Research shows that there are less endocrine cells in patients with IBS, resulting in hormone imbalances. This is a possible explanation as to why people with IBS see changes in their gut motility, have abnormal gut secretions, and experience slowed metabolism. All of these factors increase the possibility of weight gain. (10, 11)

  • Higher than normal levels of methane-producing bacteria in the small intestine: Excess methane-producing bacteria in the gut is most commonly associated with SIBO, which most often results in slow motility and constipation. Recent research shows that IBS-C patients also exhibit higher than normal levels of methane-producing bacteria in the small bowel. Weight gain is generally associated with IBS-C as opposed to IBS-D, which is more often connected to unplanned weight loss. (12, 13, 14, 15, 16)

SIBO Weight Gain

The research for SIBO weight gain is less straight forward and conclusive. However, similar to IBS-C, methane dominant SIBO has a greater likelihood of resulting in weight gain due to several factors. These factors include:

  • Slowed gut motility and constipation. (17, 18, 19, 20
  • Slowed metabolism due to hormone imbalances:
    1. Insulin – A study from 2020 found that patients with type 2 diabetes (T2D) who also tested positive for SIBO, had lower levels of insulin being secreted and worse blood glucose control than those with T2D and no SIBO. However, this didn’t always result in weight gain. (21)
    2. Thyroid Hormones – Hypothyroidism and levothyroxine therapy (the therapy used to treat hypothyroidism) are strongly associated with the development of SIBO. (22, 23) Hypothyroidism is often associated with changes in weight, specifically weight gain.

A connection between SIBO and obesity has also been drawn, however it is still unclear which comes first. A recent study found that the risk of SIBO was three times higher in obese individuals in Western countries than individuals without obesity. However this research is still new and needs additional studies to verify its truth. (24)

Another study determined a close relationship between diet and SIBO in individuals with obesity. They found that obese patients with SIBO ate more carbohydrates and refined sugar and less total and insoluble fiber. (25) This study does not test whether the diet caused the SIBO or whether the uncomfortable symptoms of SIBO lead to a more limited diet, but it brings up an interesting connection between SIBO, weight, and diet.

Now that you’ve learned the why and the science behind it, here are my suggestions for how to manage IBS/SIBO weight gain.

6 Tips for Managing IBS/SIBO Weight Gain

  • Get diagnosed. This can (and should) include consulting with a trusted healthcare professional. You’re going to hear me say this a lot on this site, but working with a gut health specialist that truly understands you and your body is going to be a game changer. The most common way of diagnosing SIBO is through a breath test. Consult your healthcare provider to figure out which test is most appropriate for you. (26, 27) Diagnosing IBS is done by eliminating all other gut related conditions first and is therefore less straight forward. This may also include rebalancing your hormones if your provider determines that is necessary.
  • Develop a treatment plan (including a diet plan). Currently, the first line of defense for IBS in particular (but it may be helpful for SIBO as well) is through diet and lifestyle changes. (28)
  • Keep a food diary. Tracking what you eat and how you feel after can provide a lot of insight into what your food triggers are. It is also important to track things like stress levels, amount/quality of sleep, fluid intake, movement, and even your menstrual cycle, as all of these play a significant role in your symptoms. An excellent resource for this is Lottie Drynan’s My Tummy Diary.
  • Manage stress. All of us have felt those “butterflies” in our stomachs when we’re anticipating something we’re nervous about. In fact, that feeling is a perfect example of the gut-brain access at work and can be a major contributor to your symptoms. Current research suggests that treating mental health conditions, such as depression, through antidepressant medication and psychological therapy has a positive impact on IBS symptoms. (29)
  • Get 7-9 hours of sleep every night. Not getting enough sleep on a regular basis is another form of chronic stress on the body and can lead to worsening symptoms.
  • Gut friendly movement. Moving your body in ways that feels good to you is important for overall health as well as gut health. Activities such as yoga, walking, swimming, and strength training are all great ways of adding movement to your day without over-stressing your body.
List of 6 tips for IBS/SIBO weight gain, plus descriptions

Final Thoughts

IBS & SIBO weight gain has a lot to do with finding the best way to manage your symptoms. The first step is to find a gut health specialist (like a Dietitian!) that you can work closely with to identify your root cause/causes. You will also want to work together to develop a treatment plan that is unique to you.

If you’ve been struggling with bloat, constipation or other IBS symptoms and need some insight into your root causes, check out my Why Am I STILL Bloated Quiz!

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Remember: this post is for informational purposes only and may not be the best fit for you and your personal situation. It shall not be construed as medical advice. The information and education provided here is not intended or implied to supplement or replace professional medical treatment, advice, and/or diagnosis. Always check with your own physician or medical professional before trying or implementing any information read here.

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Hi, I’m Grace!

A registered dietitian & gut health expert based in Portland, OR with my husband & orange tabby, Tony.


And I’ve been in your shoes!


As someone who has struggled with my own severe, chronic, & painful bloat & constipation for over 15 years, I understand what it’s like not to get answers from conventional medical support.


This is why I’ve made it my mission to help everyone who feels held back & defeated by their gut find freedom from their embarrassing symptoms FOR GOOD!

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Why am i STILL bloated?!?


Uncover the root cause of your persistent, uncomfortable bloat with this 10 Question Quiz!

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