Torwen:
Hello everyone and welcome back to the Ideal Nutrition Podcast. My name is Torwen. And I’m joined today by my co-host Aidan. Our episode today is all about SIBO. That’s small intestinal bacterial overgrowth. We’ll cover what the evidence says about it.
Aidan:
So where should we start?
Torwen:
Let’s explain what SIBO is.
Aidan:
Small intestinal bacterial overgrowth is based on the concept that most bacteria should be in the large intestine. There shouldn’t be much in the small intestine. This overgrowth occurs when it is clearly in there. There is much more of it than necessary. Often that can cause issues. That’s why it is a condition that we care about.
Torwen:
This overgrowth of bacteria can lead to digestive symptoms. These include abdominal bloating. It can also cause excessive gas and flatulence. That is normally caused by bacteria fermenting carbohydrates in the small bowel. It can also cause abdominal pain and cramping. People may notice different bowel movements. That can be either diarrhoea or constipation. People can also feel excessively full. Nausea can happen as well.
Aidan:
One reason we’re starting with what’s evidence-based and what’s not is this. There’s no gold standard diagnostic criteria. That also means prevalence rates vary a lot. It depends on what is being reported. There’s a lot of overlap with IBS-type symptoms. And I personally have seen stats showing this. Estimates range from as low as 10% of people with IBS. They go all the way up to around 80%. If it’s as high as 80%, that becomes very interesting.
If it’s as low as 10%, that’s still relevant. There’s still stuff we can do with that. I’ve gone through meta-analysis type of data. I’ve put some of that into show notes. I’ve also looked at a lot of other stuff. Some estimates look along these lines. In “healthy controls,” people who are not meant to have SIBO, we see 2.5% to 15%. That’s based on the closest we’ve got to standard diagnostic criteria. It seems far more common in older people as well.
In people with IBS-D type symptoms, the closest I’ve seen is around 35%. That’s the closest to a consensus. As I said, there’s a huge range. In people with diabetes, 30% seems a standard estimate. Coeliac disease sits around 20%. In IBD, it’s around 20% to 30%. One piece of logic is this. Prior surgery could lead to strictures. That could increase risk.
Torwen:
That’s a significant portion of people with gut disorders. It also includes other disorders. I found very similar numbers with the breath test diagnosis. It showed about 20% prevalence. Should we talk about how it’s diagnosed? Or should we talk about what can cause SIBO?
Aidan:
I reckon we go with what causes it. And there are two main mechanisms, I’d say. The first one is impaired motility. That means things go through more slowly. It gives bacteria longer to “anchor,” Then they can multiply and reproduce. If things move through the small intestine slowly, there’s more time for bacteria to grow there.
The other angle is low stomach acid. That would normally kill certain bacteria. It happens prior to reaching the small intestine. There are other angles as well. It could be coming up from the large intestine. In addition to slow motility, physical blockages can contribute. That’s where abdominal surgery can come into play.
Torwen:
This makes it quite clear that SIBO is generally considered a secondary condition. It occurs when other things are going on in the body. Or the body can’t do its natural processes. That includes protective mechanisms. We want to identify what has happened first. That’s the first step of SIBO identification, you could say.
Aidan:
Yeah, absolutely. In terms of how it’s diagnosed, as I said, there’s no gold standard. It would be so much easier if there was. There are two mechanisms. We’ve got breath testing. We also have something called a small intestine aspirate. Both of them have pros. Both of them have cons.
Torwen:
Yeah, both tests have flaws. We’ll explain what both of them do. Breath testing is a hydrogen methane breath test. You drink a mixture of glucose or lactulose. Then they measure hydrogen or methane in the breath. A rapid rise in either indicates bacterial overgrowth. The issue is that this can give a false-positive quite frequently.
Lots of things can affect the result. That includes what you’ve eaten beforehand. It also includes whether you’ve brushed your teeth. Fast transit can matter too. If you’ve got fast transit naturally, it can reach bacteria quickly. That can also affect results.
Aidan:
Yeah, specifically, it could reach the large intestine quickly. That can be completely healthy. That can be completely normal. However, that will show up as a false positive. One key thing to note is this. Thirty per cent of healthy controls in a review showed positive on a lactulose breath test. That’s a huge false positive. That’s why it’s a huge flaw. The other test is the small intestine aspirate test. It more directly measures bacteria.
It does not just measure their gas byproduct. However, it is more invasive. It involves an endoscopy. The patient needs to be sedated. A gastroenterologist passes the tube through the mouth. And then it goes into the small intestine. A small amount of fluid is suctioned out. It is then sent to a microbiology lab. They see how many bacterial colonies grow. It still has flaws. One flaw people talk about is this. It can “pick up” hitchhiker bacteria on the way through. Another issue is that SIBO isn’t always spread evenly. You might sample a “clean” spot.
That spot may not have much bacteria. However, the overgrowth could be further down. It could also be slightly higher up. That would give a false negative. Other people point out that many gut bacteria die when exposed to oxygen. Even the handling process can affect it. Because it is more invasive, it requires sedation. The risk-to-reward ratio is often considered too high. So I’ve seen many practitioners do the breath test instead. They may acknowledge its flaws. They also may not.
Torwen:
Yeah. Even with the small intestine aspirate, you have to find a gastro who is willing. They also need to believe SIBO could be the root cause. That may not always be the case. How is SIBO managed?
Aidan:
I reckon there’s one more step in the diagnostic process. I want to talk about it. If we’re going with what’s evidence based and what’s not, this matters. Some people will very willingly use the breath test. They use that as the end point. We can see the flaw though. It has too many false-positives. So how do we improve the odds? There is no gold standard. There is nothing that’s a perfect diagnosis. A gastroenterologist could add blood testing.
That could look for vitamin deficiencies associated with this. They could look at stool evaluation to test for fat malabsorption. They could do imaging tests. That checks for structural abnormalities. This could be X-rays. It could also be CT scans. Another variable is medication use. Certain medications are linked with this. They could be more likely to have low stomach acid. That could relate to certain medications too. A clinical evaluation can also help.
Torwen:
That includes whether they potentially have post-infectious IBS. Is there anything else that’s gone on in the background too?
Aidan:
Cool. How it’s managed?
Torwen:
Let’s chat about it. Antibiotics are definitely the first line approach for SIBO. Rifaximin or neomycin are the two I’ve found. They can have quite high success rates. What are your thoughts on those?
Aidan:
Yeah, that’s definitely what I consider frontline. In terms of effectiveness, what I saw in research was this. They have about 60% effectiveness. That’s for normalising breath test results. Even then, you’re like, well, that’s not incredible. Sixty percent from antibiotics isn’t incredible. Still, that’s good. It’s a step in the right direction.
One issue is recurrence. Around 45% of people have a recurrence within nine months. That’s within nine months of antibiotic use. Obviously, antibiotics have downsides. That’s particularly true for repeated cycles. That leads to a focus on the root cause. Antibiotics can be the frontline treatment. However, other things may help if it’s recurring.
Torwen:
And to bring it back, what could the root cause be? Is it PPI use? Is it causing low stomach acid? Is it slow motility? Is there any other gastro issue going on? That could be causing this. Diet strategies can be linked to antibiotic use. That’s something I would probably recommend. Let’s talk about the low FODMAP diet first.
Aidan:
Yeah, let’s start with that one. That’s the first one I see a lot of people pointing to. The low FODMAP diet involves avoiding or minimising fermentable carbohydrates. There is a list. We’ve got heaps of content on this. It’s pretty easy to find what it is. It’s also typically not something you do long term. There are reintroductions and stuff like that. It very clearly can help with symptoms. That’s particularly true for IBS-type symptoms. In terms of bloating, it can help.
If you have less fermentable carbohydrate coming in, there’s less fermentation. That should lead to less bloating. It should also lead to less gas build up. It might help reduce overgrowth a little bit. It gives them less to feed on. However, there isn’t heaps of research supporting that. It also is not a treatment by itself. As we were speaking about off air, it can help early. A lot of people find some improvement early on. Still, it doesn’t seem to solve everything.
Torwen:
I want to jump in with that. I’ve had a client come to me. They did a very low-carb carnivore-style diet. It has a similar idea behind it. The idea is that you eliminate carbohydrates. That starves these bacteria. It takes away that fuel. That’s the thought with low FODMAP. It’s also the thought with low-carb carnivore-style diets. However, they’re not long-term. Reintroduction is very important. Personalisation matters for longer-term gut health.
Aidan:
Yeah. In a way, low carb or carnivore is a simpler way of doing it. That’s up for flaws as well. Did you see the elemental diet and stuff like that as well?
Torwen:
I have. That one is a little bit different. You replace your food with a pre-digested liquid formula. You do that for 14 to 21 days. The idea is that nutrients are absorbed early. That’s within the first few centimetres of the small intestine. Then bacteria further down have nothing to eat. They will starve. I haven’t commonly seen it used in practice. Maybe that’s because it’s expensive. I don’t really know how you would access it. And I also don’t know if it makes food enjoyable.
Aidan:
Yeah, absolutely. Those are the barriers. One study I saw found a greater than 80% success rate. That was for normalising breath tests. That raises an obvious question. Why isn’t this common practice? Firstly, I never think we should overreact to one study. It’s not like we have heaps of data. Still, what we have looks promising. It also makes sense. It follows the logic of “starving the bacteria.”
Everything digests before it gets to most of this bacteria. Or it digests before it gets to where it’s likely to be. Based on that data, it looks more effective than antibiotics. That would make you think we should just do that. Downsides exist, though. It is a bit expensive. I looked into how you get it. You can order it online.
It doesn’t seem super popular. You can get powder. Then you turn it into liquid, and so on. It apparently tastes terrible. Palatability was the word that was used. It’s just not very commonly used. Still, it’s interesting to know it exists. It can be an option after antibiotics. That’s especially true if it recurs. That’s also true if you can’t find a “root cause”.
Torwen:
In 14 to 21 days, it may help. You’d have to tolerate terrible-tasting food, though. The comparison is big. Eighty percent versus 60% success is huge. With that, let’s talk about probiotics. This can be a controversial aspect of nutrition or diet strategies. It can also be controversial for diet strategies.
The reason it’s controversial is this. People argue about adding more bacteria. There is already an overgrowth in the small intestine. We’ve popped this study in the show notes. A meta-analysis has shown certain strains can help. I’m going to absolutely butcher this name. Saccharomyces boulardii and Bacillus clausii can help.
They can help clear SIBO. They can also improve symptoms. They may even help antibiotic effectiveness. However, people who took multi-strain broad spectrum probiotics reported this. They said it increased abdominal pain. They also reported increased bloating.
Aidan:
Absolutely. That review also found timing may matter. In practice, I’d consider probiotics after antibiotics. That could “help restore the balance.” It could also help prevent recurrence. I lean in favour of probiotics being worth doing. I don’t do it as something that will move the needle heaps.
Still, it can be a step in the right direction. So, key takeaways on my end are these. A lack of diagnostic criteria makes this difficult. It makes it hard to interpret. And it also makes it hard to get help in many cases. There is valid hesitance around testing. That’s especially true when the diagnosis isn’t certain. It could be many other things too. Still, it’s worth being aware of.
I can see why people would be hesitant to overdiagnose it. It still is a legitimate condition though. Going down the management path, here’s how I’d look at it. I’d probably do antibiotics first. Still, I can see logic in doing either option. That includes an elemental style diet if you wanted to. Step two is to find the root cause.
Then address it if relevant. That’s particularly important with PPIs. Low stomach acid can matter. Other surgeries can matter too. For example, a blockage can be caused by previous surgery. Sometimes they will get surgery to fix the blockage. So, look at that root cause angle as well. I view probiotics as optional. Personally, I would consider them too.
Torwen:
I think that covers most of my thoughts. If you’re a clinician listening to this, keep this in mind. You may not be super familiar with SIBO. You also may not come across it often. Use clinical reasoning with test results. Those test results can give many false positive results.
Aidan:
Absolutely. This has been episode 241 of the Ideal Nutrition Podcast. If you haven’t already, please leave a rating and review. We would massively appreciate that. Thank you for listening, as always.