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Small intestinal bacterial overgrowth, or SIBO, is one of those diagnoses that is controversial at best, overlooked at worst and often overblown on the internet. Is SIBO the same thing as IBS? Is SIBO real? How do you know if you have SIBO? And then, of course, there is the SIBO diet: is the best SIBO diet low FODMAP, SCD or low fibre? It’s controversial, conflicting and confusing!

The reason for so many unresolved questions – and conflicting opinion – is that SIBO still eludes a gold standard in diagnosis and treatment…but don’t let that fool you into thinking that there is no scientific literature on the topic. There are hundreds of research studies listed on PubMed – so the fact that SIBO is a real thing that is not up for debate.

What is up for debate, however, is how best to diagnose and even more importantly, what to do about it. It is notoriously hard to treat, with frequent relapse. And it’s high time I wrote about this condition, which is common in my nutrition practice. So let’s get started!

We’ll talk about the SIBO diet first, then dive deep into the research on what SIBO is and how it might be treated.

Is there an SIBO Diet?

Let me give it to you straight: diet alone is unlikely to improve SIBO – and dietary therapies for SIBO are poorly researched4. Elemental diets, given that they are fully absorbed, are thought to be beneficial in the ‘kill phase’ of treatment – but are also extremely unpalatable and difficult to execute in reality5. So I don’t recommend them.

We need researchers to step up and start investigating dietary protocols; however, we aren’t entirely flying blind. Different practitioners will recommend a different dietary approach based on their own clinical experience…since we don’t have a ton of evidence for our choices. So let’s explain where the approaches come from. In SIBO, it is expected that carbohydrates feed the bacteria that are overgrowing, particularly ones that are less quickly absorbed. Every time you eat, your small intestine is awash in nutrients coming from your stomach, making it difficult to avoid feeding the bacteria there.

Some believe in starving out the bacteria, while others believe that bacteria need to be fed and replicating to make them easier to kill with antimicrobials. Some opt for a low fibre, easily digestible carbohydrate approach. Think more white rice, zero beans. Others, the specific carbohydrate approach. But what is more common amongst health professionals is the Low FODMAP elimination diet, even though it hasn’t been tested for use in SIBO5.

A low FODMAP diet could help in a few ways, for example, reducing double sugars like lactose and fructose. If SIBO damages the brush border enzymes, malabsorption could occur that could lead to more fermentation and symptoms1. It will decrease the poorly absorbed fermentable carbohydrates, which may help underfeed overgrowing bacteria without being totally low carb. However, I would also encourage eliminating added sugars and low FODMAP refined starches like rice cakes in favour of whole foods like intact grains, vegetables and small portions of fruit.

A low FODMAP diet is not meant to be long term, as it may alter the beneficial bacteria in the colon – and it’s not a treatment for SIBO, just a support for antimicrobial protocols.

It’s also strongly recommended to avoid alcohol, which can decrease motility and brush border enzyme activity, and cause injury to the gut10.

Intermittent Fasting for SIBO

Something else that I rely on to help ease symptoms, and optimize the migrating motor complex cycle, is time restricted feeding. I encourage my clients to go at least 12 hours overnight without food, to allow for multiple MMC cycles. In addition, I work with my clients to craft filling and balanced meals so they can snack less; ideally, waiting 4-5 hours between meals so that the 3rdphase MMC wave will activate in between meals.

Of course, life happens. If hunger strikes, you need to honour it – and I recommend doing so with lower carbohydrate snacks like raw nuts. Similarly, if you are feeling so bloated and full that you have no appetite, I recommend honouring that too. Let your body tell you when it’s ready to eat again…or you’ll just pour more fuel on the fire.

Prokinetics for SIBO

As it is thought that motility is a key factor in bacterial overgrowth, I may often add a prokinetic to the nutritional plan. Prokinetics help encourage proper motility; there are pharmaceutical options but also natural ones!

Ginger is a gentle prokinetic that you can eat, sip or take as a supplement. I really like Traditional Medicinals Ginger Aid tea as it is an herbal grade tea. If that isn’t strong enough, I am a big fan of Iberogast, which is now back on shelves in Canada. It is a clinically-validated herbal formula that really does work. I would continue the prokinetic and time-restricted feeding beyond your antimicrobial protocol as part of your maintenance regime.

Probiotics for SIBO

Probiotics are another touchy subject in SIBO, because evidence is scarce. There are many theoretical reasons why probiotics might help:

  • may increase transit time/motility
  • may stimulate the MMC
  • may help heal gut barrier dysfunction (leaky gut)
  • may reduce hypersensitivity in the gut
  • may fight off potentially harmful microbes

In the research, probiotics may be effective in helping decrease SIBO, but may also make it worse4. Some trials have also suggested that probiotics will work well as a complimentary therapy to antimicrobial protocols3,11.

Some practitioners worry that because even beneficial microbes like lactobacillus can overgrow, that probiotics may exacerbate symptoms. However, probiotics will help to balance out any potentially negative effects of the antimicrobials on your good gut microbes.

I personally like using probiotics, given at night in the fasting state, where they won’t interfere with antimicrobials and will be exposed to many MMC waves to (in theory) reduce their ability to overgrow. Make sure you’re choosing a high quality, clinical probiotic. Of course, it’s about proceeding with caution; if they appear to make symptoms worse in a way that doesn’t subside over 4-5 days, discontinue use.

I highly recommend that you don’t do this work on your own. Working one-on-one with a registered dietitian can help ensure you are well-nourished to support healing while trying to get SIBO under control.

Looking to understand my clinical rationale for how to create a SIBO diet?

Let’s take a look at what SIBO actually is, and what causes it.

What is SIBO?

Our colon is essentially a bioreactor, with trillions of bacteria living mostly in the ascending colon. Most of these bacteria are a type called Gram-negative bacteria, and they thrive in a low or no oxygen environment. However, the closer regions of your small intestine are supposed to have relatively few bacteria along its length, less than 1000 bacteria per millilitre1,2. These bacteria are mostly Gram-positive and require oxygen3. As you draw closer to the colon, bacterial numbers grow in transition to the bacteria-rich environment of the colon2,3.

It is thought that bacteria don’t really colonize the gut in the small intestine as they do in the colon because transit time through the small intestine is so much quicker than the colon – roughly 2-5 hours in comparison to 12 hours or (much, much) longer in the colon. The trillions of bacteria survive in your colon by eating whatever is left after you digest and absorb; which isn’t much, considering that you absorb 80-95% of everything you eat and drink when your gut is working normally. It’s mostly fibre, maybe a bit of leftover fat or protein or something poorly digested like lactose.

The small intestine is different: it is flooded with nutrients every single time you eat. So, if bacteria start to overgrow, there’s plenty to feed them…making further overgrowth possible. Typically, the diagnostic point for small intestinal bacterial overgrowth is when bacterial numbers reach 100,000 – 1,000,000 bacteria per millilitre1,2,4,5.

Which bacteria overgrow matters too: some metabolize bile salts, which could lead to fat malabsorption and foul diarrhea1,2. Others may not lead to elimination issues but cause severe bloating. Yet others might produce toxins like ammonia that cause inflammation and can cause gut barrier dysfunction, or mimic other conditions1,2.

How common is SIBO?

Since there is no consensus on the gold standard for diagnosing SIBO, it’s a controversial diagnosis with wildly varying reported rates in the studies1,4,5. It is estimated that prevalence of SIBO increases as we get older, from about 6% in younger adults to as high as 15% in older adults1.

What Causes SIBO?

Of all of the contributing factors, slow intestinal transit or motility, appears to be a primary issue1,2. As soon as you swallow, you give up conscious control of your gut movement (except for the pooping part!) and your enteric nervous system coordinates the flow of a consistent wave that propels gut contents along in a timely fashion, sweeping waste and bacteria along with it.

Except, it isn’t always timely. Poor motility can occur for many reasons, from hypothyroidism to diabetes, gut surgery including gastric bypass, low fibre or high fat intake, or an overgrowth of methane-producing microbes known as archea, that can cause constipation1,4. When motility is slow, bacteria in the small intestine are not swept clear and may be more likely to overgrow1.

This slow motility gives bacteria a chance to colonize and overgrow. It is thought that SIBO is more often due to an extension of colonic bacteria into the small intestine, with fewer instances of overgrowth of normal small intestine bacteria such as lactobacillus2.

The Migrating Motor Complex: Your Gut’s Rinse Cycle

When you are in the post-absorptive state…meaning that you have already digested and absorbed your last meal, a motility cycle called the Migrating Motor Complex (MMC) is activated. This is meant to clear out any debris in the gut and move it on through. Phase 1 of the cycle has no contractions, whereas phase 3 has the strongest contractile activity, which typically begins in the stomach7.

The strong phase 3 MMC occurs perhaps every 90-120 minutes when you are in the fasted state, and how long it takes to ‘turn on’ post-meal is going to differ between individuals1,5,7. The intestinal cells release a hormone called motilin, which is associated with the initiation of the strong phase 3 MMC waves, in addition to a sensation of hunger7.

However, your body has many ways of controlling the bacterial content of your gut. Another is the high stomach acid that will kill many microbes; it is thought that low stomach acid can be one of the predisposing causes of SIBO1,2. This can occur because of H.pylori infection, aging or medication use1,2. So for those of you on proton pump inhibitors…be aware. This is one medication that I try and support my clients in weaning off in all but the most serious of circumstances because quite frankly, they don’t always fix the issue at hand and can lead to dysbiosis or even infection with dangerous microbes such as Clostridium difficile.

Other Potential Contributing Causes of SIBO1,2,4,5

  • Frequent antibiotic use
  • Digestive surgery, particularly loss of the ileocecal valve due to resection
  • Digestive diseases such as celiac disease or irritable bowel syndrome
  • Regular alcohol consumption
  • High sugar and refined starch diet
  • Age
  • Other disease states such diabetes, renal failure, hypothyroidism

SIBO Symptoms

The symptoms of small intestinal bacterial overgrowth are pretty darn non-specific…which is why a thorough diagnostic process is so important. They include1,2,4,5

  • Abdominal pain/discomfort
  • Bloating and abdominal distention
  • Diarrhea (more common)
  • Constipation (less common)
  • Gas, reflux and belching
  • In more severe cases: vitamin deficiencies and weight loss

It’s also worth noting that SIBO has been associated with both fibromyalgia and rosacea, so if either one of those is an issue for you, you might want to investigate the bacterial connection5.

SIBO Breath Testing

There has been great debate about how best to test, what constitutes a positive test and therefore how common SIBO is. It was previously thought that sampling the small intestinal fluids was the best method, but it’s fairly uncommon because putting a tube down your throat is downright unpleasant. In addition, many bacterial species found in the gut don’t survive outside the body, making them difficult to culture and assess1,3. So typically, we rely on breath testing.

Breath testing usually measures both hydrogen and methane exhaled after consuming a test dose of either glucose or lactulose1-3,5. These tests can produce plenty of false negatives; only recently has consensus around diagnostic protocol been proposed, although this consensus statement is still being debated1,2,4,5,8.

How Can You Tell If it’s IBS or SIBO?

The symptoms of IBS and SIBO have a great deal of overlap, leading to a considerable amount of study correlating the two. These studies are conflicting: some believe that SIBO and IBS are one in the same, or that one causes the other. For example, SIBO can cause damage to the intestinal cells, reducing the activity of brush border enzymes that metabolize double sugars like lactose and fructose – two FODMAPs that can lead to diarrhea in those with IBS2. The degree of SIBO in IBS has been estimated anywhere between 4-78%, with some believing that maybe a third of those with IBS have SIBO3,4,6. Because IBS has strong diagnostic criteria, it is easier to diagnose; however, it could be wise to do SIBO testing to rule it out as a root cause of the IBS symptoms.

Severe SIBO can lead to inflammatory damage to the intestinal cell, making it difficult to distinguish from celiac disease – and it is thought that those with unresponsive celiac disease might want to consider SIBO as a cause2.

Treatment for SIBO

Antibiotics are the common therapeutic choice, most often rifaxmin plus neomycin for addressing archea overgrowth1,2,4,5. Rifaximin is a unique antibiotic that is not absorbed into the blood stream and is thought to kill bacteria in the small intestine, leaving the colon relatively untouched1,2,4,9. Rifaximin may even improve numbers of beneficial lactobacilli and Bifidobacterium in the gut9. However, symptom relapse is very common – perhaps in as little as three weeks1,2,4. In addition, this antibiotic protocol is very expensive here in Canada.

There is also an herbal antimicrobial available that I use in my practice, Candibactin-AR and BR; one trial suggests that it is an effective alternative to rifaximin4,5.

A Natural Approach to SIBO

Whew! So there you have it. Maybe the longest blog post I’ve ever written…on a complex and controversial topic. It’s worth noting that all of this advice is here to empower you – because not all practitioners have adequate knowledge of the topic. But no one should attempt to diagnose or treat SIBO on their own. Get yourself an amazing team so you are effectively supported in reaching your best possible health. If you need a good dietitian, we’ve got you covered!

Reference Note: All statements are referenced, but I have switched around the post a bit, meaning you might have to search for the reference hyperlink. However I assure you…it’s there!