Your guide to Small Intestinal Bacterial Overgrowth or SIBO

Updated: May 22

Closely associated with irritable bowel syndrome, SIBO or small intestinal bacterial overgrowth is exactly that, an overgrowth of bacteria that normally reside in the lower part of the gut (colon), but have migrated into the small intestine.

There, they encounter food that’s less broken down than it would be in the colon, which they eat and ferment into gas resulting in horrible bloating and abdominal discomfort.


Symptoms can be debilitating and unfortunately recurrence is common but anyone with gut issues, irritable bowel syndrome, food sensitivities, autoimmune disorders and malabsorption symptoms (e.g. anemia) should be assessed for SIBO. Here's an important summary of this frustrating condition.


Woman with a balloon indicating a bloated abdomen

What are the symptoms and key indicators of SIBO?

Irritable bowel symptoms such a....

  • Bloating and gas

  • Belching and flatulence

  • Abdominal pain and/ or cramps

  • Diarrhea or constipation or both

Other symptoms include:

Woman clutching her abdomen in discomfort

What are the key indicators of SIBO?

You are more likely to have SIBO if you experience any of the following:

  • A dramatic but short term improvement in IBS or gut symptoms after a course of antibiotics.

  • Chronic gut symptoms occurred after a long term course of broad spectrum anti-biotics (eg. amoxicillin, penicillin, erythromycin, doxycycline, ciprofloxacin or norfloxacin).

  • GI symptoms worsen with probiotic use or after consuming fermented foods like kefir, kombucha, and sauerkraut.

  • Symptoms are also aggravated with increased fibre in your diet or of take prebiotics (as food for commensal bacteria).

  • Chronic gut symptoms developed after taking proton pump inhibitors (usually used for reflux & heartburn eg. losec or omeprazole) or after taking opiates (eg. oxycodon, heroin, morphine, methadone, codeine and pethidine).

  • If you have coeliac disease but report insufficient improvement from a strict gluten-free diet.

  • You experience chronic low iron or ferritin levels with no other cause.

  • Your symptoms started after a bout of viral gastroenteritis or bacterial food poisoning (post-infectious SIBO or IBS).

  • Your chronic gut symptoms started after an abdominal surgery.

  • You have an underlying condition such as endometriosis, type1 diabetes, multiple sclerosis, Crohn's disease, Coeliac disease or hypothyroidism.

What diseases and disorders are associated with SIBO?

What causes SIBO?

Poor gut motility and altered bowel flow is considered to be the main factor.


Poor gut motility means that food moves more slowly than it should through the intestines. It is thought to be due to a disturbance in the migrating motor complex (MMC), a pattern of contractions that occur in the gastrointestinal tract between meals.


This cyclic, recurring wave of movement sweeps food and bacteria out of the small intestines. It occurs every 90 minutes or so when your stomach is empty.


An altered MMC or gut motion can be due to a number of reasons but examples include adhesions and scar tissue from previous abdominal surgery, endometriosis, and nerve dysfunction.


A high stress lifestyle, certain medications, long periods of sitting, and frequent snacking can also interfere with the MMC and gut motility.


Man feeling unwell after eating fast food

What causes the bloating and excessive gas?

The bacteria in your gut produce certain gases when they eat and digest food, particularly food containing fermentable carbohydrates. These gases are not made by the human body itself but by the microflora or bacteria within your gut. In fact, bloating after meals is directly related to the production of gas by these micro-organisms.


Excessive amounts of bacteria leads to more gas being produced. Bacteria in the small intestines encounter food that’s less broken down than it would be in the colon, further fueling gas production. The gas builds up distending the bowels and abdomen, sometimes to the point you look pregnant!


The type of gas produced depends on the unwelcome microorganisms present.


What are the 3 types of SIBO?

Hydrogen-dominant, Methane-dominant and Sulfide-dominant SIBO are the three types.


Excessive hydrogen gas producing bacteria tend to promote diarrhea, as it pulls water into the bowel.

Those with an overgrowth of methane producing bacteria, tend towards constipation.

Organisms that create hydrogen sulfide (H2S) gas as a byproduct damages the cells of the body and typically experience diarrhea, though constipation can occur also. Only a very small portion of SIBO cases are hydrogen sulfide dominant.


How do you know if you have SIBO?

SIBO is diagnosed from a thorough health history, the presence of risk factors or key indicators and/or a SIBO Breath Test.


The SIBO breath test measures the hydrogen and methane gas produced by organisms in the small intestine that has diffused into the blood, then the lungs for expiration. They are graphed over a 2 to 3 hour period and then compared to a baseline.


The test involves having to be on a special (little to no carbohydrate) diet for 1-2 days prior to the test. A baseline is taken just prior to consuming a sugary solution of glucose or lactulose. Then every 20 minutes for 2 to 3 hours the methane and hydrogen levels are measured.


An accurate test requires you to adhere strictly to the preparatory diet. Plus, it is best to avoid probiotics, antibiotics and any anti-microbial herbs for at least 2 weeks prior. Proton pump inhibitors (such as omeprazole or Losec for reflux), laxatives, high dose magnesium or vitamin C should also be avoided for 2 to 3 days prior.


If you wish to learn more about the SIBO breath test then check out this full instructional guide or visit our lab testing page. Some gastrointestinal specialists are becoming more aware of this condition and may also be prepared to arrange this test. The cost is around $215 NZD.


How do you treat SIBO?

There are a number of options:

1. Prescription Antibiotics - specifically Rifaximin (brand name Xifaxan). This antibiotic is used to kill the excess bacteria.

2. Natural Herbal Antimicrobials - oral supplements that contain natural herbs, oils and spices that also have the ability to kill bacteria and other microorganisms.

3. Special low carbohydrate diets - to starve the bacteria.

4. Probiotics - certain types can reduce symptoms.

5. Prokinetics - supplements or drugs that improve the motility of the gut and sweep the bacteria from the small intestine back down into the colon.


These can be used alone or in conjunction with each other.

For more detailed information on how to treat SIBO and prevent a recurrence visit...

Natural Treatment Options for SIBO and 10 ways to prevent SIBO or a recurrence


Herbal supplements

Why does SIBO often recur even after treatment?

Common reasons for an recurrence include:

  • A structural issue - such as adhesions and scar tissue from surgeries or endometriosis which slow gut motility.

  • Poor ileocecal valve function - the valve at the junction between the large and small intestine can interfere with the movement of bacteria.

  • The presence of an underlying condition that slows gut motility, such as type I diabetes, celiac disease, Crohn’s disease, or hypothyroidism.

  • Inadequate treatment - this can be due to use of the wrong type of antimicrobial, not enough time on the antibiotics or antimicrobials, or too low a dose to kill the bacteria. Poor follow-up care with no probiotic or prokinetic use are additional reasons.

  • Eating too regularly or too late at night so that the MMC doesn't occur frequently enough. The MMC contractions only occur between meals, when there is no food in the stomach, so frequent snacking won't help.

  • Lack of movement and long periods of sitting. Sitting reduces blood flow to the digestive tract, which slows GI motility.

  • There is an underlying pathogenic bacteria due to food poisoning. The bacteria that cause food poisoning such as E. coli, Campylobacter jejuni, Shigella, and Salmonella produce a substance called cytolethal distending toxin (CDT) , which can damage cells in the intestines and impair the MMC in certain people.

  • Excessive stress - stress down regulates digestion, inhibits motility and slows food transit in the stomach and small intestines.

With our current Western lifestyle of high stress, processed foods, drug and medication use, SIBO is on the rise. Although it has been known about for the last 50 to 60 years, only recently has SIBO become widely accepted. The benefits of addressing a small intestinal bacterial overgrowth are huge and should always be considered in those suffering gut symptoms, malabsorption, allergies and autoimmune conditions.


The diagnosis of SIBO is relieving for many IBS sufferers as there are effective treatment options, meaning a lifetime of suffering is completely unnecessary.


However, addressing SIBO can be challenging, with recurrences common. Working with a trained practitioner who is highly familiar with the treatment of SIBO is recommended.


Keen to work with me to address your IBS, SIBO, leaky gut or poor gut health?

Head here for more information.


Information provided from Steven Sandberg-Lewis & Allison Siebecker for the Functional Medicine University.


For more info on specific SIBO diets please go to Dr Siebecker's website.


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