All About SIBO:

Why the low FODMAP diet may not be working for you?

By Lizzie Gralton

Finding Your Balance Dietetics

July 2025

I have seen some clients be mis-diagnosed with IBS or just diagnosed with IBS when they is other things going wrong in their digestion. Having the CORRECT diagnosis is essential so you are able to get complete relief of symptoms and food freedom back!

What is SIBO?

Have you ever heard of SIBO? It stands for Small Intestinal Bacterial Overgrowth - condition that occurs when excess bacteria begin to grow in the small intestine, a place they’re not meant to thrive in large numbers.

SIBO can be tricky to diagnose, and the underlying causes can vary from person to person. While research is still evolving, we’re learning more about how and why it develops — and why a Low FODMAP diet may not always be the answer.

How does “Healthy” Digestion Work?

Let’s do a quick overview of the digestive system to understand how SIBO fits in:

  1. Mouth – Mechanical digestion starts here, with chewing and saliva breaking food down.

  2. Oesophagus – Transports food to the stomach.

  3. Stomach – Produces acid and enzymes to break food into smaller particles.

  4. Small Intestine – Where most nutrient absorption takes place.

  5. Large Intestine/Colon – Where fermentation occurs and stool is formed.

  6. Rectum & Anus – Waste exits the body.

In a healthy gut, fermentation of prebiotic fibres (which feed beneficial bacteria) mostly happens in the large intestine. But in SIBO, fermentation begins too early — in the small intestine — leading to an overgrowth of bacteria in the wrong place.

Common Symptoms of SIBO

SIBO can cause a wide range of symptoms, including:

  • Bloating and abdominal discomfort

  • Nausea

  • Excessive gas

  • Fullness after eating small amounts

  • Indigestion and reflux

  • Diarrhoea or constipation

  • Fatigue

  • Unintended weight loss

  • Vitamin deficiencies (especially B12 and folate)

  • Skin breakouts like acne

In some cases, SIBO can also lead to:

  • Steatorrhea (fat in the stool), which appears pale, oily, floaty, and foul-smelling

  • Malnutrition and deficiencies, especially fat-soluble vitamins A, D, E, and K

  • Low protein levels

  • Bone loss and osteoporosis

  • Weakened immune system

If you notice these signs, particularly changes in stool, speak with your doctor or gut health specialist right away.




What are Suspected Causes of SIBO?

There isn’t one single cause, but some common risk factors include:

  • Low stomach acid, especially from long-term use of antacids or PPIs (proton pump inhibitors), or after infections like H. pylori

  • Digestive surgeries such as gastric bypass

  • Slow gut motility, often from IBS, chronic constipation, or low thyroid function

  • Structural abnormalities in the digestive tract

  • Overuse of antibiotics, which can disrupt the natural gut microbiome

    Treatment Protocol:

    Step 1: See a Specialist

    Start by working with a healthcare provider who understands gut health — ideally a dietitian like myself who focuses on digestive issues.

    Step 2: Rule Out Other Conditions

    It’s important to rule out other conditions like coeliac disease, IBD, or lactose intolerance before testing for SIBO.

    Step 3: Take a Breath Test

    The most common diagnostic tool is the Lactulose Breath Test, which measures hydrogen and methane gas levels in your breath after drinking a sugar solution. Elevated levels indicate fermentation happening in the small intestine — a sign of bacterial overgrowth. Important to follow instructions such as avoid fermentable food list day before and day of test, no antibiotics 4 weeks prior and a couple more as per instructions on site. (Lim, J., Rezaie, A. 2019).

    I often recommend this home test from breathtest.com.au because it’s easy to do and well-explained.

    If still unsure then a referral to Gastroenterologist for scopes to complete biopsy to get a more obvious picture is recommended.


Treatments

The first line of treatment is usually a course of antibiotics like Rifaximin, prescribed by your GP. The goal is to reduce bacterial overgrowth while identifying and addressing the root cause of why it developed in the first place.

Ongoing treatment is best managed with a specialist who can guide you through the next phases, including diet, supplements, and long-term prevention.]

Why Low FODMAP Might not be enough?

While the Low FODMAP diet can be helpful to reduce symptoms like bloating, gas, and abdominal pain, it doesn't treat the root cause of SIBO. It may provide temporary relief, but without addressing the bacterial overgrowth, symptoms often return.

Post-Treatment Nutrition: What I Recommend as an Accredited Dietitian in this Space

Once antibiotic treatment is completed, I work with clients to manage symptoms and prevent recurrence through nutrition. My approach may include:

  • A modified low FODMAP diet (short-term)

  • Small, frequent meals

  • Reducing sugar and starchy carbs

  • Limiting processed and packaged foods

  • Supporting gut motility with lifestyle strategies

The goal is to minimise fermentation in the small intestine while slowly reintroducing fermentable fibres to rebuild a healthy gut microbiome.

Supplements I May Consider with you

Depending on individual needs and test results, I may also recommend:

  • Vitamin B12, D, and K (if deficient)

  • Iron and Zinc

  • Probiotics — specific strains, timing, and duration are key (some can actually be harmful for your treatment).

SUMMARY

SIBO is more than just bloating — it’s a condition that needs careful diagnosis and tailored treatment. If you’ve tried the Low FODMAP diet and you're still experiencing gut issues, it may be time to dig deeper. As a dietitian with a gut health focus, I help people uncover the root cause of digestive symptoms and build a plan that works for their unique body. Need support with SIBO or ongoing gut issues? Book a consultation and let’s work through it together.