What is SIBO? (and how do you know if you have it?)

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Do you suffer with chronic diarrhoea or constipation?

Experiencing regular bloating and abdominal pain?

Or perhaps you’ve eliminated certain foods from your diet but haven’t seen much improvement in your symptoms….

You might have Small Intestinal Bacterial Overgrowth, or SIBO for short.

What is SIBO?

SIBO is defined as excessive bacteria in the small intestine.
Naturally, our digestive tract is full of bacteria but the bulk of them are found in our large intestine, not our small intestine.(1)

In comparison to our large intestine, the small intestine has relatively low levels of bacteria. This is the space in our digestive system where food mixes with digestive juices and nutrients are absorbed into the bloodstream.

When bacteria from the large intestine overflow into the small intestine and take over, they can interrupt our normal digestive processes, leading to:

– Malabsorption of nutrients, particularly fat-soluble vitamins and iron
– Stomach lining damage
– Inflammation
– And symptoms commonly associated with Irritable Bowel Syndrome (IBS).

Bacteria in our digestive tract help with digestion and absorption of nutrients by feeding on the foods we eat. When bacterial numbers are too high in the small intestine, unpleasant symptoms including gas, bloating, pain, diarrhoea, and weight loss can occur.(2)

How do you get SIBO?

SIBO tends to occur when normal bodily functions that keep our bacteria inside our large intestine are disrupted.

Two of the most likely predisposing factors include a reduction of gastric acid secretion, and problems with the natural muscle movements of the small intestine that move food through the GI tract.

Low Gastric Acid

Gastric acid suppresses the growth of ingested bacteria, limiting bacterial counts in the upper small intestine. So when gastric acid secretion is reduced there is an increased risk for SIBO. This can occur with the use of histamine type 2 receptor blockers (H2RAs) or proton-pump inhibitors (PPIs), or it can develop after a case of Helicobacter pylori.


Ageing is another risk factor for developing SIBO. As we age, the digestive tract slows down and gastric acid secretion is reduced. Studies show 15% of non-hospitalized adults over the age of 61 have SIBO, which increases to more than 30% in disabled older adults. In comparison, less than 6% of people 24-59 years old are typically diagnosed with SIBO.(3)

Structural Changes, Conditions and Diseases

Other risk factors include small bowel motility disorders, structural abnormalities of the gastrointestinal tract from surgeries or chronic digestive diseases, impaired gastric peristalsis, disturbances of the immune function of the gut, strictures, intestinal pseudo-obstruction, coeliac disease, Type 2 diabetes, scleroderma and polymyositis.(2)

People who are immunodeficient, whether due to an abnormal antibody response or T-cell response, are also prone to bacterial overgrowth.(4)

TABLE 1: Common Risk Factors For SIBO

— Small intestine diverticula
— Small intestine strictures (radiation, medications, Crohn’s disease)
— Surgically created blind loops
— Resection of ileocecal valve
— Fistulas between proximal and distal bowel
— Gastric resection

Motility Disorders
— Gastroparesis
— Small bowel dysmotility
— Coeliac disease
— Chronic intestinal pseudo-obstruction

Irritable Bowel Syndrome
Metabolic Disorders
— Type 2 Diabetes
— Hypochlorhydria

Organ System Dysfunction
— Cirrhosis
— Renal failure
— Pancreatitis
— Immunodeficiency states
— Crohn’s disease
— Coeliac disease
— Malnutrition

— Recurrent antibiotics
— Gastric acid suppression

— Chronic alcohol use

There are many risk factors and contributors to the development of SIBO. It’s important to visit your doctor to rule out any serious medical issues, determine the cause of your SIBO and work with your health professionals to determine the most suitable treatment.

Signs and Symptoms of SIBO

SIBO symptoms are very similar to symptoms of IBS and other gastrointestinal disorders. SIBO should be ruled out before diagnosing IBS.(5)

Signs and symptoms vary from person to person, and in severity, but often include a mix of:

● Abdominal pain/discomfort
● Abdominal distension
● Diarrhoea
● Flatulence
● Weakness
● Nausea
● Bloating
● Vomiting
● Malnutrition
● Weight loss
● Joint pain
● Fatigue
● Rashes
● Acne
● Eczema
● Asthma
● Depression
● Rosacea

The frequency and severity of symptoms typically increase with the extent of overgrowth and inflammation. However, some symptoms may be from the underlying cause of SIBO too.

Other symptoms can reflect complications of SIBO, including malabsorption, nutritional deficiencies, and metabolic bone disorders.

Long-Term Health Effects Of SIBO

Aside from the symptoms you might experience day to day with SIBO, the long term consequences of unmanaged SIBO can be quite severe. (2) These include:

● Unintentional Weight Loss
● Steatorrhea (fat malabsorption)
● Vitamin/Mineral Deficiency
— Fat-soluble vitamins (A, D, E, K)
— Vitamin B12
— Iron
● Vitamin Excess
— Folate
● Hypoproteinemia/Hypoalbuminemia
● Decreased Xylose Absorption
● Osteoporosis

These long-term health effects are why it’s important to work with your GP to determine the underlying cause of your SIBO.

How is SIBO diagnosed?

There is no current gold standard for diagnosing SIBO but breath testing is the most common method to assess overgrowth because it’s simple, safe and non-invasive. However, there are some limitations to these tests as differences in bacteria types from person to person can influence their response.

Currently, the most common test for SIBO is the lactulose or glucose hydrogen breath test. No optimal protocol or proper interpretation guidelines for those with rapid or delayed gastric emptying have been developed yet.

However, most health professionals follow this testing procedure:

1. Follow a pre-test diet
2. Fast overnight
3. Take a baseline breath sample
4. Drink the carbohydrate mix (usually 10g of lactulose, or 50-80g of glucose in 120-200ml of water)
5. Collect a number of breath samples every 15-30 minutes over a period of 3-4 hours after drinking the mix.

The breath testing method relies on the bacteria to consume the carbohydrate and produce a gas byproduct, hydrogen, that can be measured via your breath. Though 10% of adults may not be colonized with the bacteria capable of producing hydrogen, resulting in a false negative test result.

The effectiveness of the tests are influenced by recent use of antibiotics, and the effects of H2RAs and PPIs on breath test results remain controversial.(2)

A positive result is indicated by an increase from the baseline fasting hydrogen concentration to a value greater than 10–-12 parts per million (ppm) after a 50g glucose load or greater than 20 ppm following lactulose, during the first 90 minutes of the test. Or when a ‘double peak’ of hydrogen occurs in the test results.

How do you treat SIBO?

There are three main aspects of SIBO treatment:

1) Correct the underlying cause,
2) Dietary management,
3) Treatment of the overgrowth.

Currently, the first point of treatment is antibiotics. This helps to kill the problem bacteria, but also kills the healthy bacteria necessary for proper digestive function. (6)

Antibiotics reduce or eliminate the bacterial overload and reverse the mucosal inflammation associated with overgrowth and malabsorption. But antibiotics can be expensive, there is potential for resistance, drug interactions, and unwanted side effects. Plus, more often than not, antibiotic treatment alone requires multiple courses, which is less than ideal for our gut health.

In fact, one trial demonstrated an average duration of symptom improvement of only 22 days, which translates into a need for at least 12 courses (presuming 7 days) of antibiotics per year to provide persistent symptom relief. (2)

Another study published in the American Journal of Gastroenterology found that SIBO patients treated with antibiotics have a high recurrence rate and that gastrointestinal symptoms increased during the recurrences.(7)

The most effective management of SIBO appears to be via antibiotics and diet. In a study published in the American Journal of Gastroenterology, people with Coeliac disease and SIBO were treated with a more holistic approach featuring a combination of antibiotics, prescription medications for worms and parasites, and a change in diet. All patients reported their symptoms had subsided after this treatment.(8)

So what should you do? First, it’s important to visit your GP to identify if there’s an underlying cause. Then a visit to your Dietitian is a must so you can ensure you’re getting all your nutritional needs met while eating a diet to help reduce your SIBO symptoms and get your body back into balance.

Consuming probiotics and probiotic-rich foods may also be beneficial. A pilot study from researchers at the Center for Medical Education and Clinical Research in Buenos Aires, Argentina, found probiotics have a 30% higher efficacy rate than metronidazole for individuals with SIBO. (9)

An initial dose of antibiotics, followed by probiotic therapy may be most effective.

The SIBO Elimination Diet

In addition to antibiotics, probiotics, combating nutrient deficiencies, and identifying the underlying cause, changing your diet is also important for long-term SIBO management.

The aim is to give the digestive system time to repair itself, remove foods that fuel unwanted bacterial growth, ease inflammation, and consume a diet rich in nutrients to support repair and restore balance to the gut flora.

Those with SIBO may find relief by following a Low FODMAP elimination diet. FODMAPs are highly digestible carbohydrates that are easily fermented in the digestive tract. This fermentation process involves bacteria, as the FODMAP foods feed the bugs and help them thrive.

High FODMAP foods are generally healthy to consume for the average person, but may cause digestive problems in those with SIBO and IBS. High FODMAP foods include garlic, onion, legumes, artichoke, wheat, apples, pears, cauliflower and cashews.(10)

It’s important to undertake this diet with the help of a qualified Dietitian so you are eating as much variety as possible and meeting your nutrient needs. Particularly for those with weight loss and/or vitamin and mineral deficiencies.

Eating smaller meals more frequently, reducing sugar intake, and limiting processed foods and starchy carbohydrates is also recommended to help starve and kill off unwanted bacteria.

Limiting lactose- and fructose-containing foods (as part of the Low FODMAP diet) can also help reduce symptoms because those with SIBO may develop a lactase and fructase deficiency due to inflammation of the small bowel. (2)

Dietary changes are critical to the long term management of SIBO but must be done so under the supervision of a dietitian to ensure nutritional needs are met.

A SIBO Diet Meal Plan


This is what a day’s worth of food may look like on the SIBO diet:

Breakfast: Eggs with sauteed spinach and tomato and a cup of bone broth

Lunch: Salad of leafy greens, cucumber, carrot, zucchini, squash and pumpkin with chicken

Dinner: Walnut-crusted salmon with green beans, capsicum, carrots and kale

Snacks: Handful of blueberries, fresh pineapple, dark chocolate, nut butters, lactose free yoghurt.

At first it may seem like there isn’t much you can eat, but there are a lot of healthy, wholesome foods you can enjoy while sticking to the SIBO diet.


Supplements for SIBO

Your dietitian or GP may advise you to take some nutritional supplements during SIBO treatment depending on your needs. These may include:

● Vitamin B12
● Vitamin D
● Vitamin K
● Iron

● Zinc
● Probiotics
● Digestive Enzymes

However, research is still in its infancy with regards to what supplements may improve symptoms and keep SIBO at bay.

Some herbal remedies have been discussed in research, such as oregano oil, berberine extract, wormwood oil, lemon balm oil and Indian barberry root extract, but as yet, none of them have been sufficiently tested for safety or efficacy.

If you experience any of the listed SIBO signs and symptoms on a regular basis, don’t hesitate to see your GP to get a confirmed diagnosis, treatment plan, and referral to see a dietitian.

Larina Robinson

Larina Robinson is a Wholefood Dietitian, author and founder of The Body Dietetics. Specialising in gut health, food intolerances and alternative diets, Larina empowers people to embrace a diet unique to their own dietary needs and supports them to find freedom from long-term digestive complaints.

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