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The Low FODMAP diet explained

What is the Low FODMAP diet?

If you’ve been struggling with digestive issues such as bloating, gas, pain, or altered bowel habits (ranging from diarrhoea to constipation), you may have come across the low FODMAP diet.

The low FODMAP diet was developed by researchers at Monash University in Australia, who identified a group of short-chain carbohydrates (FODMAPs) that aren’t absorbed well in the gut. They found that, for some people with irritable bowel syndrome (IBS), foods that are high in FODMAPs can trigger symptoms. Research shows that 50-80% of people with IBS experienced improved gastrointestinal symptoms on a low FODMAP diet1,2.

The low FODMAP diet is a well-researched (and widely promoted) approach to managing IBS symptoms.

What does FODMAP stand for?

FODMAP stands for:

Fermentable
Oligosaccharides
Disaccharides
Monosaccharides
and Polyols.

The oligosaccharide group includes fructans (found in foods like wheat and garlic) and GOS (found in foods like legumes and nuts).

The disaccharide group includes lactose (found in some dairy products like milk and yoghurt).

The monosaccharide group includes fructose (found in foods like honey and apples).

The polyol group includes sorbitol (found in foods like avocado and some sugar-free products) and mannitol (found in foods like mushrooms and cabbage).

What is irritable bowel syndrome (IBS)?

Irritable bowel syndrome (IBS) is a chronic (ongoing) gastrointestinal disorder that affects how the gut functions. IBS is generally not harmful, although it can be uncomfortable and affect quality of life.

Common symptoms include:

  • Bloating
  • Excessive gas (wind)
  • Abdominal pain or cramping
  • Changes in bowel habits (constipation, diarrhoea, or a mix of both)
  • Urgency to open the bowels

If you think you may have IBS, it’s important to see your doctor for a full check-up and diagnosis. Other conditions can cause similar symptoms, so it’s important to rule these out.

How does the low FODMAP diet work?

The low FODMAP diet has three phases.

  1. Elimination Phase (2-4 weeks)

High FODMAP foods are swapped for low FODMAP alternatives.

Unlike with most other elimination diets, serving size matters. For example, when eaten in one sitting, three spears of green asparagus is considered low FODMAP. Five spears of green asparagus however, is considered high in the FODMAP group fructose.

  1. Reintroduction Phase (8-12 weeks)

If your symptoms improved during the elimination phase, the individual FODMAP groups will be re-introduced one at a time using a structured protocol. This helps to identify your personal trigger foods.

  1. Personalisation Phase

Once your triggers have been identified, your nutritionist can work with you to develop a personalised eating plan. You will only need to avoid foods that affect you, so the diet isn’t unnecessarily restrictive.

Low FODMAP diet considerations

The low FODMAP diet isn’t simple. It’s best to enlist the help of a Registered Nutritionist or Dietitian who specialises in this area.

An alternative approach, or a modified low FODMAP diet, is likely to be needed for children, young people and for anyone with a history of disordered eating3.

It’s not advisable to extend the elimination phase of the low FODMAP diet beyond 4 weeks. This is because:

  • Many healthy foods are restricted
  • The diet can negatively affect the healthy bacteria in your gut (your microbiome)4.
  • It’s rare for someone to react to all FODMAP groups. Permanently avoiding all high FODMAP foods is usually unnecessary.

 Starting the low-FODMAP diet

A Registered Nutritionist or Dietitian trained in the low FODMAP approach can help you:

  • Decide if the low FODMAP diet is right for you
  • Understand and follow the diet safely
  • Make sure you’re getting enough nutrients
  • Identify your personal food triggers
  • Make the personalised phase of the diet sustainable long-term

They should also consider other factors that may trigger IBS symptoms, for example:

  • Fluid and fibre intake
  • Possible non-FODMAP food triggers e.g. coffee, alcohol, spicy food
  • Overall diet quality
  • Sleep
  • Exercise and stress management5
  • The gut-brain connection6.

Need help with the low FODMAP diet?

Before jumping straight into the low FODMAP diet, I like to make sure it’s the right approach for you. After taking a full health history and discussing your current eating habits, I’ll explain the pros and cons of the diet in a way that’s relevant to you. Together, we can decide whether to:

  • Begin the low FODMAP diet
  • Try a modified, gentle version of the low FODMAP diet
  • Focus on other nutrition or lifestyle factors first.

Sometimes improvements seen during the elimination phase are due to a reduction of gluten or dairy proteins (rather than FODMAPs). Where relevant, I’ll suggest adding additional steps into the protocol to check for this. My aim is always to find the least restrictive way of eating that allows you to manage your symptoms.

 

Need personalised nutrition advice?
Elly McKenzie is a New Zealand-based nutritionist specialising in practical, evidence-based support for gut health, coeliac disease, irritable bowel syndrome, food allergies/intolerances, and general nutrition (including healthy eating, high cholesterol/blood pressure and pre-diabetes).Elly McKenzie Nutritionist Mount Maunganui

Consultations are available in person at her Mount Maunganui clinic (Tauranga) or across Aotearoa via secure Telehealth. Book a consultation or get in touch to learn more.

 

References

  1. Wanyu Yang, Qian Liu, Kangqi Jiang, Huizi Tan,Exploring the dual effects of the Low-FODMAP Diet: Symptom relief and psychological stress in adult IBS patients – a systematic review and meta-analysis, Food Nutrition, Volume 1, Issue 1,2025,100014,ISSN 3050-8436Top of Form.
  2. Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. 2014 Jan;146(1):67-75.e5. doi: 10.1053/j.gastro.2013.09.046. Epub 2013 Sep 25. PMID: 24076059.
  3. O’Brien L, Kasti A, Halmos EP, Tuck C, Varney J. Evolution, adaptation, and new applications of the FODMAP diet. JGH Open. 2024;8(5):e13066.
  4. Zhang H, Su Q. Low-FODMAP Diet for Irritable Bowel Syndrome: Insights from Microbiome. Nutrients. 2025 Jan 31;17(3):544. doi: 10.3390/nu17030544. PMID: 39940404; PMCID: PMC11819959.
  5. Huang KY, Wang FY, Lv M, Ma XX, Tang XD, Lv L. Irritable bowel syndrome: Epidemiology, overlap disorders, pathophysiology and treatment. World J Gastroenterol. 2023 Jul 14;29(26):4120-4135. doi: 10.3748/wjg.v29.i26.4120. PMID: 37475846; PMCID: PMC10354571.
  6. Peters SL, Yao CK, Philpott H, Yelland GW, Muir JG, Gibson PR. Randomised clinical trial: the efficacy of gut-directed hypnotherapy is similar to that of the low FODMAP diet for the treatment of irritable bowel syndrome. Aliment Pharmacol Ther. 2016;44(5):447-59.
  7. Monash