What is the SIBO diet and how does it work?

If you’re grappling with the digestive pain and discomfort of SIBO, keeping symptoms under control can be a minefield. Here’s what you need to know.

While having a large gut microbiome can be beneficial to your immune system, having too much of it could just bring more harm than good – especially if it’s in the wrong place.

Although comparatively little is known about SIBO compared to other digestive complaints, research shows there are some diet strategies that may help alleviate symptoms.

What is SIBO?

An abbreviation for Small Intestinal Bacterial Overgrowth, nutritionist Edwina Ekins says SIBO can be difficult to diagnose and is not yet well understood.

While experts have estimated there are up to 30 per cent of Australians suffering from Irritable Bowel Syndrome (IBS), the numbers for SIBO patients are still not as clear-cut.

“A basic explanation of the condition is an abnormal increase in bacteria in the small intestine, which usually only contains a small amount,” Edwina says.

“It is actually the large intestine that should contain most of the gut microbiome and a larger number of bacteria.”

What are the symptoms of SIBO?

A condition usually diagnosed by a GP or a gastroenterologist, Edwina says the symptoms for SIBO are gastrointestinal and can be similar to those of IBS.

“This may include deficiencies such as vitamin B12, constipation, diarrhoea or bloating,” Edwina explains.

Diet Solutions dietitian Nick Dunn adds other common symptoms may also include wind, reflux, headaches, joint pain, inflammation and fatigue.

According to a 2007 study, SIBO could also cause problems such as chronic diarrhoea, weight loss, and osteoporosis.

How can SIBO be treated?

“A SIBO breath test is one of the four ways of testing for this condition,” Edwina explains.

“It’s non-invasive and looks to measure a response or a reaction where a rise in exhaled hydrogen or methane could indicate an overgrowth of bacteria in the small intestine.”

But Everyday Nutrition dietician Joanna Baker adds this diagnosis can be tricky and the tests aren’t always reliable.

“Given that SIBO is a condition involving the overgrowth of bacteria, antibiotics targeting these bacteria are the most effective treatment,” Joanna says.

“Once it has been treated, I like to see where the dust settles in terms of symptoms and then address symptoms either empirically or by addressing food sensitivities.”

However, Joanna says SIBO can have a high incidence of recurrence with potential risk factors including inflammatory bowel disease, a history of surgeries and PPI usage.

How do SIBO diets work?

SIBO diets aim to reduce inflammation and bacterial load in the digestive system through the elimination of certain foods.

Nick says while there are several SIBO diets, but they all generally work the same way – by restricting the carbohydrates that gut bacteria feed on.

“This means there is less fuel for the bacteria to consume, and therefore often an individual will experience fewer symptoms,” Nick says.

Can the low-FODMAP diet help SIBO symptoms?

A low-FODMAP diet can help SIBO sufferers identify food triggers by avoiding certain carbohydrates (fermentables, oligosaccharides, disaccharides, monosaccharides and polyols) and gradually reintroducing them to their diet.

Developed by Monash University, Edwina says this could help manage SIBO and reduce gastrointestinal symptoms.

“Certain carbohydrate foods, specifically those containing fermentable carbohydrates known as FODMAP foods, can exacerbate symptoms in both SIBO and IBS,” Edwina explains.

“These foods contain a type of sugar called a short-chain carbohydrate that is poorly absorbed in the small intestine, causing digestive stress in some people.

“However, it’s important to understand this is more of a dietary intervention to reduce symptoms rather than a ‘diet’ and should only be done short term with the help of a qualified professional.”

This diet is relatively safe, effective and could even be modified to meet individual needs, Joanna adds.

“It puts the person in control of treating and managing symptoms.”

Foods to avoid

• Milk, ice cream and yogurt
• Cereal and bread
• Vegetables, including artichokes, asparagus, beans, cauliflower, garlic, lentils, onions and peas
• Fruit, including apples, cherries, dried fruits, pears and peaches; high-fructose corn syrup, honey and soft drinks.

Foods to eat

• Eggs and meat
• Almond milk
• Brie, camembert, cheddar and feta
• Gluten-free biscuits, noodles and pasta
• Oats, peanuts, quinoa, rice, seeds
• Vegetables, including broccoli, carrots, cucumbers, eggplant, leafy greens, olives, potatoes, pumpkin, tomatoes and zucchini
• Fruit, including blueberries, grapes, oranges, pineapple and strawberries.

What is the specific carbohydrate diet?

Another diet that may help SIBO is the specific carbohydrate diet, which limits carbohydrates to only those that are easily digested.

There have been very few clinical studies into SCD and most support comes from testimonials.

Foods to avoid

• Potatoes
• Grains, including rice, wheat, corn, quinoa, millet
• Processed meats
• Most dairy
• Most legumes
• Processed sugar and processed foods.

Foods to eat

• Most unprocessed, fresh or frozen fruits and juices
• Most vegetables
• Most fresh meats, eggs
• Homemade fermented yoghurt, some natural cheeses
• Soaked dried legumes
• Nuts and nut butters
• Herbs and spices.

While it’s reported that SCD and a low-FODMAP diet are sometimes combined to manage SIBO, one study found the latter statistically had significant improvement in symptoms.

Originally published in December 2021. Updated in November 2023.