Intersection of IBS, SIBO & the Low FODMAP Diet

Hey Friends.

Today’s post includes a bit of “alphabet soup”: SIBO, IBS & FODMAPs. I will start with a brief introduction of SIBO and commonly asked questions about this disorder.  I will then provide a few low FODMAP diet updates too!

Let’s start with SIBO, shall we?

What is SIBO?  SIBO is a condition where both aerobic and anaerobic bacteria over grow in the small intestine. Typically, the small intestine contains low levels of bacteria unlike the large intestine which harbors a diverse ecosystem of microbes. Our gut microbes play a role in health and disease. Important positive functions of microbes include: degrading carbohydrates for fuel, creating vitamins for good health and maintaining normal function of our immune system.

What are the symptoms of SIBO? Symptoms mimic those found in irritable bowel syndrome including: bloating, abdominal distention, gas, pain, fullness after eating, and alteration of  bowel habit (constipation, diarrhea or alternating).

When SIBO occurs are we full of ‘bad bacteria’? SIBO occurs when we have bacteria in the wrong place versus having too many of the wrong kind of microbes. Though it is possible that certain microbes vs. others are more problematic (cause more symptoms) in the small bowel. More research is needed!

Dysbiosis is a condition where there is an imbalance of microbes. Dysbiosis may present with an abundance of potentially pathogenic (disease causing) bacteria versus probiotic (health promoting) microbes. This can occur in your colon or small intestine. We all have our own personal gut microbial fingerprint which makes navigating this science a bit trickier.

Are SIBO and IBS related? I  think of SIBO as IBS on steroids. SIBO and IBS could be separate conditions or perhaps a disorder on the same spectrum. IBS and SIBO present with similar symptoms though I find in my clinical practice SIBO patients experience symptoms of greater severity. I asked William Chey, MD, a leading US gastroenterologist and world-renowned authority on food intolerance from University of Michigan to weigh in on this discussion w/ me.

Kate: Do you think SIBO and IBS are really the same disease on a spectrum?

Dr. Chey: I have a somewhat different view. IBS is a symptom based condition consisting of abdominal pain and altered bowel habits. I believe that there are likely a number of “diseases” for which we don’t currently have biomarkers, which present with symptoms that are consistent with the diagnosis of IBS. Consider this, 20 years ago, we didn’t understand that a small percentage of “IBS” patients actually have Celiac disease or microscopic colitis or dyssynergic defecation. Now it is widely recognized that all of these diseases can mimic IBS. I believe that SIBO is another IBS mimic. I also believe that even in the absence of a formal diagnosis of SIBO (>10×5 CFU/ml), quantitative or qualitative alterations in the gut microbiome can cause IBS symptoms.

Kate: What are some clinical features you assess in your patients that would prompt you to order a SIBO breath test?

Dr. Chey: Risk factors like diabetes, scleroderma, immune deficiency disorders, neuromuscular disorders, etc. make me consider SIBO early in the work up of a patient with pain, cramping, bloating, flatulence or diarrhea.

Kate: Do you have a dietary approach you recommend for your SIBO patients and why?

Dr. Chey: My primary approach to the treatment of SIBO is a course of antibiotics. To reduce systemic side effects and the development of antibiotic resistant extra-intestinal bacteria, I prefer to use non-absorbed antibiotics like rifaximin. I often use adjunctive dietary therapy following antibiotics – I focus on the low FODMAP diet. Though this is not an evidence based strategy for SIBO, I do think there is a biologically plausible reason this the diet may offer clinical benefits and increase the durability of response to a course of antibiotics for SIBO. We know that the low FODMAP diet offers clinical benefits to the symptoms of IBS which are often indistinguishable from SIBO. Further, we also know that FODMAPs are important prebiotics for a wide range of bacteria. Thus, it is reasonable to hypothesize that reducing dietary FODMAPs might slow recurrence of SIBO. Of course, this remains to be proven is methodologically rigorous clinical trials.

I appreciate these very thoughtful answers from Dr. Chey and fully agree with them. Let’s continue with other questions that arise frequently about SIBO.

Where can I find accurate and evidenced based resources for SIBO? To be honest, I get pretty worked up about the misinformation that abounds on the Internet about SIBO and the overall lack of research in this area. With this, I feel terribly sorry for the SIBO sufferers out there trying find treatments to feel better. Unfortunately,  there is a lack of consensus amongst GI docs and other healthcare professionals when it comes to the testing, diagnosis and the treatment of SIBO. This leaves patients stumbling to find answers on their own.  I follow Mark Pimentel’s research (he’s active on Twitter @MarkPimentelMD), attend key GI conferences such as Digestive Disease Week to learn about evidence based research in this area, and gather as much science-based research via Pub Med  I can get my hands on. When working with your healthcare provider, ask about their treatment approach. Their answer should include: determine cause of SIBO, treat with non-absorbed antibiotics (there is some evidence for herbal therapies too and/or an elimination diet), and adjust diet to the patient’s personal tolerance often with a reduction in fermentable carbohydrates. Also, any supplement recommendations should have science to support their use. Be wary of practitioners that want to sell you $$$ worth of supplements. When doing any online research (sometimes this just adds to your stress– so limit your time online!), be sure the site is reputable and science-based.

How do you get tested for SIBO? I understand the often arduous process it takes to get a diagnosis for SIBO. I was diagnosed with this condition back in 2003, 10 years after an intestinal resection and was very miserable for almost 2 years prior to getting treatment.  Getting the diagnosis took firing a couple GI docs and finding a new one that would listen and understood SIBO. If you have SIBO or think you might have SIBO…the best thing you can do is find a gastroenterologist that understands this condition.

Should you take probiotics when you are taking antibiotics for SIBO? A recent study published in 2017 conducted a meta-analysis (a statistical analysis that combines the results of multiple studies) and systematic review of current evidence to assess the efficacy of probiotics in preventing or treating small intestinal bacterial overgrowth (SIBO).  The results showed that the probiotics group showed a significantly higher SIBO decontamination rate than the non-probiotic group (RR=1.61; 95% CI, 1.19-2.17; P<0.05). The hydrogen gas level was significantly reduced among probiotic users too. Probiotics were associated with a reduction in abdominal pain scores but they have little effect on daily stool frequency. Given the review of this meta-analysis, I have started to recommend probiotics supplements during rifaximin therapy. But, of course, each individual should follow the recommendations of their personal health care provider.  The study can be found here.

What diet should you follow when you have SIBO? This is the million dollar question and honestly, there is little research in this area. However, given the majority of SIBO sufferers fulfill the diagnosis of IBS –and the low FODMAP diet is an evidenced based therapy for IBS, the low FODMAP diet is my first line therapy for SIBO.  I await research in this area. Any diet that restricts poorly absorbed or short chain carbs that small intestinal bacteria will gain easy access to, ferment and allow them to grow –will likely contribute to symptom benefit. Diet should be individualized and should be the least restrictive to maintain quality of life and adequate nutrition. There are many VERY restrictive diets recommended for SIBO and I do not feel the majority of individuals need to highly restrictive with the diet.  In my experience working with thousands of patients with SIBO, the bulk of them improved on the low FODMAP diet. I have had a handful of patients that had difficulty with starches and fibers. Working with a dietitian to guide diet therapy is a must. Additionally, remember diet is one part of the solution for SIBO. Many SIBO patients put so much pressure on themselves and on the importance of diet that their stress level prohibits them from attaining good health. Treating SIBO requires (in my opinion) a multi-faceted treatment plan. More on this to follow.

What test should you undertake for SIBO–glucose or lactulose?  Glucose offers greater accuracy per a couple papers: Saad, R  2014 Dec;12(12):1964-72. Rana, SV Digestion 2012;85:243–247

But…I thought I would ask Dr. Mark Pimentel from Cedars Sinai as he is the true expert on breath testing in my opinion.

Kate: I am reviewing the literature and most papers I am reading favor the glucose breath test over lactulose saying it is the most accurate. Yet,  I realize that the glucose can miss distal sibo. Are you still in favor of lactulose testing for this reason?  

Mark Pimentel: “The recently published north American Consensus of experts suggest lactulose because it is more likely not to miss SIBO.”  The North American Consensus paper Dr. Pimentel is referring can be accessed here.

In my opinion, I often favor the glucose test for my patients with a very sensitive tummy, who tend to have rapid onset of symptoms post eating and are diarrhea predominant. I encourage glucose testing for these patients to avoid the laxative effect of lactulose (it speed intestinal transit & functions as a laxative).

What is the best treatment for SIBO? Antibiotic (pharmaceutical, herbal or elemental diet) to induce remission. Identify underlying cause of SIBO (when possible) and treat (ie–identify celiac, treat issues such as fecal loading or severe constipation), and maintaining remission w/ discrete meal times & spacing, motility medications, adequate bowel regimen or elimination habits –constipation or fecal loading reduce movements in small intestine and likely contribute to relapse. Correcting any nutritional deficiencies is important too. I typically encourage testing Vitamin D (fat malabsorption often occurs with SIBO), B12, ferritin, zinc for starters and supplement as needed. Individualized therapy is key!

Rifaximin, a poorly absorbed  drug with unique properties is typically the first line therapy for SIBO with a positive hydrogen test. When methane gas is elevated, a combo of rifaximin and neomycin, may have greater efficacy as noted in the study noted here.

Rifaximin is active against pathogenic and non-pathogenic bacteria in the bile-rich small bowel (it’s soluble in bile) and its low water solubility makes it active only against highly susceptible bacteria, primarily anaerobes, in the water filled colon.

Rifaximin may also impart some anti-inflammatory effects in the gut or the function of the gut microbes (ie gut microbe metabolism, adherence and/or virulence). We are still learning more about how this particular medicine helps SIBO patients.

What if my SIBO test is negative but I felt miserable during the test? Discuss with your doctor whether you should be treated empiraclly with antibiotics or consider further work-up.

What symptoms are associated with methane + sibo?  Those who are methane + sibo are more than 5 times more likely to be constipated, the more methane gas, the more severe the symptoms, and treatment may require dual antibiotics. One study found here revealed better eradication of methane + sibo with neomycin + rifaximin. Other resources for methane:

  • Rezaie, A How to Test and Treat Small Intestinal Bacterial Overgrowth An Evidenced-based Approach. et al Curr Gastroenterol Rep 2016; 18: 8.
  • Kunkel D et al. Methane on breath testing is associated with constipation: a systematic review and meta-analysis. Dig Dis Sci. 2011;56:1612–8.

What about hydrogen sulfide gas? Can microbes make hydrogen sulfide gas? Yes, they can! You may find in individuals with hydrogen sulfide production that the breath results are completely flat-lined (meaning zeros on both hydrogen and methane levels throughout the 90 minute testing time). The microbes that make hydrogen sulfide gas use up all the hydrogen to make hydrogen sulfide so the hydrogen expelled from the lungs during the test is undetectable. I asked Dr. Pimentel a few questions about hydrogen sulfide…

Kate: Hydrogen Sulfide gas.  Would love you to  provide some info to my blog followers. Do you think testing for this is coming soon to the consumer? 

Dr. Pimentel: “While H2S is really exciting there is no device to measure this commercially yet. We are working to get one out there but not for at least a year.” 

In a recent abstract presented at the DDW meeting in Chicago in May 2017, elevations in hydrogen sulfide gas were associated with diarrhea and fatigue.  More to come as the research evolves in the gut microbiome, health/disease and diet research!

Okay…if you are still with me…

FODMAP updates: I updated my low and high FODMAP checklists. Why? Because, sadly bananas were re-tested at Monash University and found to be high FODMAP for the full ripe banana.  You can eat an unripe banana (not too many of my clients are psyched about that) BUT you can still have up to 1/3 of a ripe banana–so I added that to my updated list. Updated checklists can be printed for personal use….but if you are a FODMAP newbie–try to work with a registered dietitian knowledgeable in the low FODMAP diet to guide you. The diet is most effective when adhered to correctly.  If you are a low FODMAP diet follower or health professional seeking low FODMAP educational handouts check out my free resources here.

Oyster mushrooms tested…and are LOW fodmap…yay, for that! And did you see those little baby canned corn (the kind that you find in Chinese dishes), they are low FODMAP too! I really like the Monash U low FODMAP app to learn the latest food updates. My team at For a Digestive Peace of Mind are also in the background working on new updates for my low FODMAP grocery guide app–the goal is to add more brand name items that appear low FODMAP per ingredients–along with certified low FODMAP foods too. (All proceeds of my app are being used to provide free resources for those with IBS.)

Congratulations if you read all of this! What other science topics would you like me to cover? I am all ears.