Title: What is Small Intestinal Bacterial Overgrowth Syndrome (SIBO?)
Small Intestinal Bacterial Overgrowth Syndrome (aka SIBO) is a term used by many to describe symptoms of generalized abdominal bloating and discomfort... What is it really and how accurate are the available diagnostic tests?
-- Symptoms --
Many patient encounters about abdominal bloating often start like this: "Jess (yes, I encourage my patients call me by my first name), I am sure that I have SIBO". And while I completely, 100% validate and understand that the person in front of me is experiencing symptoms that are real, I am not always so sure that their self-diagnosis of SIBO is the correct diagnosis. It's not that I am discounting their symptoms, the symptoms are real... it's that I worry about misdiagnosis and how this can lead to expensive unnecessary testing and treatments that may not work. And I totally get it! When I "google" the symptoms of IBS, SIBO is the first article that pops up and it is so convincing! I completely understand how many of us come to this conclusion.
Where I come in, is helping us to better understand if there are any symptoms that are considered "red flags" that require further medical testing. In the absence of "red flags", we are often left with functional conditions like Irritable Bowel Syndrome (IBS) and Dysbiosis. How do we parse out if we truly have SIBO and how effective are the diagnostic tests for SIBO?
According to the Mayo Clinic, SIBO is characterized by (1):
Loss of appetite
Abdominal pain (red flag)
Nausea
Bloating
An uncomfortable feeling of fullness after eating (red flag)
Diarrhea
Unintentional weight loss (red flag)
Malnutrition (red flag)
Aside from generalized abdominal bloating and discomfort, patients with SIBO experience persistent diarrhea, rapid unintentional weight loss and abdominal pain that lasts more than a few days (1). These are considered to be red flags. If you are experiencing these symptoms, it is important that you seek medical evaluation.
While we may experience some of these symptoms from time to time, they are not specific to SIBO. There are a wide variety of conditions that cause similar symptoms, which is why it is important to speak to a medical provider to help you to determine the true underlying cause. If you are experiencing these symptoms frequently, then it is very important that you visit a healthcare provider.
When does SIBO typically occur? SIBO most commonly occurs after abdominal surgery (like bariatric procedures), in patients with abdominal scar tissue from prior surgery, and in those of us living with certain conditions like Type 2 Diabetes, Crohn's, Inflammatory Bowel Conditions, Scleroderma (a rare collagen disorder), or gastroparesis (1). While children with short-gut syndrome can also be diagnosed with SIBO, this article focuses on adults as Lifestyle Medicine Maine does not treat children.
-- Controversy --
It is important to note that the diagnosis of SIBO remains controversial in the medical literature because the most common tests used to diagnose SIBO are not sensitive nor specific, meaning that our current tests are not accurate. The only reliable test is invasive: a scope placed through the mouth, down the throat and threaded into the small intestine to get a sample of the fluid. This comes with risks. A medical provider will help to determine if this test is appropriate for you. Currently, most of us are being treated empirically, meaning that we are making an educated guess without invasive testing.
But just because the diagnosis is controversial, that doesn't mean that people don't experience real symptoms. The symptoms of patients who report self-diagnosis of SIBO often overlap with irritable bowel syndrome (aka IBS) (7). IBS does not cause unintentional weight loss or malnutrition. In constipation pre-dominant IBS, we sometimes experience an uncomfortable feeling of abdominal fullness that is often related to not having had a bowel movement. Quickly increasing fiber when transitioning to a plant-predominant dietary pattern is a common cause of uncomfortable sensation of fullness and resolves when we reduce our fiber intake. It is important to gradually increase fiber in the diet so as to not create discomfort. Make sure to speak to a medical provider if you are unclear on the cause of your symptoms.
Symptoms of IBS include:
"Abdominal pain, cramping or bloating that is related to passing a bowel movement
Changes in appearance of bowel movement
Changes in how often you are having a bowel movement
Other symptoms that are often related include sensation of incomplete evacuation and increased gas or mucus in the stool" (8).
-- SIBO Treatment --
Treatment for SIBO is typically with antibiotics, which comes with inherent risks. Taking potentially unnecessary antibiotics can lead to antibiotic resistance and in some cases cause an overgrowth of "bad bacterial" like C. Difficile (a difficult to treat bacterial diarrheal infection). The trouble is that while many of us who are treated with antibiotics report a short term benefit, when put to the test in clinic trials, taking antibiotics for presumed SIBO can lead to worsening symptoms four months later (6).
-- SIBO Diagnosis --
Diagnosis is classically made through a breath test. The problem is that around half of people who test positive on breath testing do not actually have SIBO (these are false-positive results) (4). The idea is that glucose should normally be absorbed at the beginning of the intestine (after it leaves the stomach) (2). In SIBO, the presence of excessive bacteria is thought to ferment this sugar, leading to absorption of fermentation bi-products into the blood stream that are then exhaled through the lungs (2). The breath test is looking for changes in the concentration of certain substances the air that we exhale (2).
What causes a false-positive SIBO test? Oversimplified, these tests cannot tell us where the glucose in our food is being fermented and absorbed. In SIBO, the presumed problem is with an overgrowth of bacteria in the small intestine that are fermenting glucose. These breath tests are unable to differentiate glucose that is being fermented in the small intestine versus in the large intestine (AKA, the Colon). And for the record, we need to eat carbohydrates (which are broken down to glucose when we eat) like fresh fruit, vegetables, intact whole grains and beans for optimal health.
More about SIBO testing. The original breath test evaluated for lactulose, but when tested for validity (meaning how well it predicted the actual presence of SIBO compared to actual gastric aspirate) was not accurate (3). Breath testing was then transitioned to evaluate for glucose-based hydrogen and methane testing, which again turned out to be an unreliable diagnostic test (3)(4)(5).
What am I saying here? It didn't matter whether people had a positive or negative breath test because neither actually reflected the actual amount of bacteria in the small intestine. The researchers actually labeled the glucose to see where it was being absorbed and another team physically put a tube down people's throats into their small intestine to sample the bacteria to determine if the breath testing was accurate (3)(4)(5). Simply put, breath testing is not reliable.
To complicate the issue, the amount of bacteria in the small intestine doesn't often correlate with symptoms (4)(5). The type of bacteria plays a more significant role (5). When researchers take people who are eating adequate dietary fiber and switch them to a lower fiber diet (more processed foods high in flour and sugar), they develop symptoms characteristic of SIBO and irritable bowel syndrome (aka IBS) (5).
You see, when we eat food, we feed the microbes in our gut. Feed the microbes with fiber-rich plant foods and the colonies that benefit us grow, improving bowel symptoms. Take away the fiber-rich plant foods and symptoms often return. How quickly you might ask? We can see changes in as little as 1 week (5).
As always, what do I think? If you have having symptoms, then it is important to speak to a medical provider about them so that you can get an accurate diagnosis. Breath tests for SIBO are unreliable and do not correlate with symptom severity, do not accurately predict how many bacteria we have in the small intestine, nor do they predict the type of bacteria present. What we eat matters most when it comes to cultivating a healthy microbiome, which means that we need to be eating a diversity of high-fiber plant foods and fermented foods.
If you have been diagnosed with irritable bowel syndrome (IBS) or functional abdominal bloating, then research suggests that this may be more of a reflection of the types of foods being eaten and/or lack of adequate fiber-rich foods in the diet (5).
Here at Lifestyle Medicine Maine, we help people transition towards a high-fiber plant predominant dietary pattern to improve the microbiome. If you know what you should be doing, but you aren't sure how to actually implement those changes, then schedule a free initial consult with Lifestyle Medicine Professional Jessica Krol, FNP, DipACLM here at Lifestyle Medicine Maine to get started.
References
Small intestinal bacterial overgrowth (SIBO). Mayo Clinic. (n.d.) https://www.mayoclinic.org/diseases-conditions/small-intestinal-bacterial-overgrowth/symptoms-causes/syc-20370168
Small Intestinal Bacterial Overgrowth: Nutritional Implications, Diagnosis, and Management. Adike, et al. Gastroenterology Clinics of North America. (2018) https://doi.org/10.1016/j.gtc.2017.09.008
Does a glucose-based hydrogen and methane breath test detect bacterial overgrowth in the jejunum? Sundin, et al. Neurogastroenterology and Motility. (2018) https://doi.org/10.1111/nmo.13350
Scintigraphy Demonstrates High Rate of False-positive Results From Glucose Breath Tests for Small Bowel Bacterial Overgrowth. Lin, et al. Clinical Gastroenterology and Hepatology. (2016) https://doi.org/10.1016/j.cgh.2015.07.032
Small intestinal microbial dysbiosis underlies symptoms associated with functional gastrointestinal disorders. Saffouri, et al. Nature Communications. (2019) https://doi.org/10.1038%2Fs41467-019-09964-7
Antibiotics increase functional abdominal symptoms. Maxwell, et al. American Journal of Gastroenterology. (2002) https://doi.org/10.1111/j.1572-0241.2002.05428.x
Small intestinal bacterial overgrowth as a cause for irritable bowel syndrome: guilty or not guilty? Aziz, et al. Current Opinion in Gastroenterology (2017) https://doi.org/10.1097/mog.0000000000000348
Irritable Bowel Syndrome (IBS). Mayo Clinic. (n.d.) https://www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/symptoms-causes/syc-20360016
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