What is SIBO? (Hint: It's not what we thought!)

SIBO stands for Small Intestinal Bacterial Overgrowth. Sounds fairly self-explanatory, right?

Wrong.

For years, the functional and the conventional medicine spaces have been treating SIBO as a condition of overgrowth - ie. there are too many bacteria growing in the small intestine.

There is a myth that the small intestine should be ‘sterile’. In reality, the large intestine contains the majority of our microbiome, but the small intestine has its own, unique, microbiome. [1]

A 2019 study showed that the symptoms we associate with SIBO are actually linked to the level of dysbiosis and reduced diversity in the small intestine, rather than the quantity of bacteria. [2]

The same study showed that a group of healthy volunteers who were given a high-fibre diet actually tested positive for SIBO, but were entirely asymptomatic. This further demonstrates that it is not the amount of bacteria that is the issue, rather the makeup and balance of the small intestinal microbiome.

What is dysbiosis?

Gut dysbiosis is a imbalance in our gut bacteria, often with the reduction of our ‘good’ gut bacteria, and an overgrowth of our ‘bad’ bacteria.

Our ‘good’ bacteria are so important for our health and wellbeing, with huge effects on our hormones, mental health and immune health. If these bacteria are reduced in number, then some opportunistic ‘bad’ bacteria who are normally present in our guts in smaller quantities can take over.

These bacteria can promote a state of disease in the body, and have been implicated in the development of diseases in including cancer, autoimmunity, inflammatory bowel disease and Alzheimer’s disease. [3]

Diet is the most common cause of dysbiosis, with a typical Western diet being low in fibre and high in saturated fats and sugars.

Antibiotic use is another incredibly common cause. Antibiotics kill bacteria the good stuff as well as the bad, and leave space for the bad guys to overgrow. There is a positive correlation seen between recent antibiotic use and SIBO onset, which makes a lot of sense when you consider SIBO as a condition of dysbiosis rather than a condition of overgrowth.

7 other causes of dysbiosis — Other causes of dysbiosis

What symptoms does SIBO cause?

SIBO causes all the same gastrointestinal symptoms you also associate with IBS and Functional Dyspepsia:

Bloating
Abdominal pain/discomfort
Abdominal distension
Diarrhoea/constipation/mixed bowel habits
Flatulence
Burping
Acid reflux
Steatorrhoea/fat malabsorption
Low or high appetite

You many experience one, many or none of these symptoms.

SIBO varies from IBS and Functional Dyspepsia in that is it is more likely to cause systemic symptoms, affecting the whole body. These include:

Weight loss
Fatigue
Low mood
Headaches
Joint pain
Muscle twitching
Histamine intolerance
Rosacea
Acne
Nasal congestion
Restless leg syndrome

[4]

Again, you may experience several or none of these.

As we all have different microbiomes, different root causes and different immune responses, our symptoms are rarely the same. With my SIBO, I experienced only a couple of gastrointestinal symptoms (with the main one being severe abdominal pain), but had every single one of the listed systemic symptoms at some point during my journey.

Why does SIBO cause symptoms?

Small intestinal dysbiosis hinders our ability to digest and absorb our nutrients effectively. As 70% of our immune system is found in the gut, SIBO triggers a huge inflammatory response, further driving digestive dysfunctions. This can also cause ‘leaky gut’ (or increased intestinal permeability) as this inflammation causes holes in our intestinal barrier which food particles and bacteria can escape through, further fuelling the immune response.

This inflammation can cause damage to the brush border enzymes we use to digest our food, causing carbohydrate malabsorption. These carbohydrates are then the perfect feast for the bacteria, who ferment them and produce gas. These happy and well fed bacteria then cause more inflammation, which causes increased malabsorption…and so the cycle continues.

The bacteria can also deactivate bile salts, leading to fat malabsorption. This can lead to bile acid diarrhoea - greasy, yellow looking poo that often floats.

They love stealing our nutrients and vitamins, and even using them to nourish and grow themselves. This is particularly relevant to iron, B12, and the fat soluble vitamins A, D, E and K which are often low in SIBO sufferers. [5]

This combination of factors means that SIBO not only causes localised gut symptoms, but also systemic symptoms which can impact on your whole body!

How is SIBO diagnosed?

Not very well.

The ‘gold standard’ for SIBO diagnosis is small intestine aspirate where basically, they take a sample of bacteria from your small intestine during an endoscopy. This is both very invasive and not foolproof due to the potential for contamination with oral bacteria as the sample travels up through the mouth. It also only tests the bacterial composition of the duodenum (the top part of the small intestine). Not a lot of use if your problem is in your ileum (the bottom part of the small intestine)!

Mostly, therefore, we use breath testing, a non invasive method which involves drinking a sugar solution (either glucose or lactulose) and then collecting your exhaled breath at regular intervals for 2-3 hours. The breath is then tested for hydrogen and methane levels, and high levels of either of these gases mean you have SIBO.

Or maybe not…

The test is extremely unreliable due to the large differences in transit time from person to person. In fact, the test was originally developed to measure transit time from mouth to large intestine, not to test for SIBO at all. [6] Lactulose can accelerate transit time, so it is very likely that many of the peaks that we associated with SIBO are actually a false positive. Equally, for those with very slow motility, there may be false negatives. Essentially, the test is invalid unless we know our orocecal transit time.

How is SIBO treated?

If your problem is that you have too many bacteria in the small intestine, then antibiotics make sense as a treatment. You start with too many bacteria, antibiotics reduce the number of bacteria, and hey presto! There’s your problem solved. Only it hasn’t worked like this, and conventional treatment strategies have very limited success with the treatment of SIBO.

Recent research has found that the majority of the bacteria found in SIBO patients are Klebsiella and E.Coli - both from the proteobacteria family. [7]

Antibiotic resistance is increasingly being seen in proteobacteria and so often antibiotics are unsuccessful at removing these bacteria from the gut. [8] Antibiotics are, however, very successful at killing a lot of the ‘good’ bacteria, further perpetuating a dysbiotic state in the small intestine.

In fact, it is perfectly possible for a SIBO test to show improvement, but symptoms to get worse (it happened to me, several times).

Dysbiosis is a state best treated with a microbiome rebuilding strategy - one of prebiotics, probiotics and postbiotics. That's not to say that antimicrobials don't have their place, but they should not be the first line of treatment against SIBO.

So, to knock this myth on the head now, PROBIOTICS WILL NOT FEED SIBO. There is not one study implicating lactobacillus or bifidobacterium in SIBO. In fact, lactobacillus and bifidobacterium can outcompete the bacteria which are causing symptoms in your gut.

People sometimes react to probiotics because not all probiotics are the right fit for all people, so it can take a degree of trial and error to discover what works for you.

There is also no evidence that you can starve the SIBO, despite many sufferers being on a Low FODMAP diet.

These diets can be useful for symptom management for 4-6 weeks, but any longer than that they have been shown to negatively affect the microbiome and worsen dysbiosis. [9] A study has shown that depriving the microbiome of fibre leads to degradation of mucous membrane and enhanced pathogen adhesion and susceptibility. [10]

Prebiotics can be tricky to tolerate initially, but a low and slow approach should build tolerance, and supplements can always help if your diet is still quite restricted. I loved PHGG powder when I was struggling to tolerate prebiotics - a Low FODMAP fibre supplement which didn't increase my symptoms. I started with 1/4 of a teaspoon per day, and built up from there to 5g.

Postbiotics are beneficial compounds produced by probiotic bacteria during fermentation. They are naturally produced in a healthy gut, but it can also be helpful to supplement these while you are healing your gut to help the terrain favour a state of microbial balance.

And of course, none of these will work if the root causes (brain-gut axis dysfunction, low digestive capacity, liver dysfunction, thyroid dysfunction, inflammation, endometriosis, medications, etc) aren’t fully addressed.

Does SIBO always come back?

There is another widely held belief that SIBO is a relapsing condition that always returns. This is a myth.

People often (but not always) feel immediately better after a course of antibiotics, only to then relapse again within weeks or even days.

This is simply because they haven’t got the root cause of the issue. If you treat the root cause effectively, and return the gut microbiome to a balanced state, SIBO will not return.

How can SIBO cause IBS or Functional Dyspepsia?

IBS and Functional Dyspepsia are umbrella terms that really describe a collection of symptoms, rather than a specific disease. They are often the diagnoses given when you have seen a doctor, all the tests are clear and they don’t really have any answers for you.

SIBO can certainly be an underlying driver in both IBS and Functional Dyspepsia as there is huge symptom overlap between the three conditions. If you treat your SIBO effectively, you will likely find that your IBS and Functional Dyspepsia symptoms reduce, or even disappear entirely.

To sum up:

SIBO is more of a state of dysbiosis than one of overgrowth, and treatments are much more effective when we treat it as such.

Focus on treatments which get to the bottom of your individual root cause, and only then treat the dysbiosis. Remember, most people have more than one root cause (I had at least six), so if you’re struggling to make headway, look to other potential additional root causes.

This format will help you not only knock your SIBO on the head, but stop it coming back.