FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols — short-chain carbohydrates that the small intestine absorbs poorly. In sensitive individuals, such as people with IBS, they can cause bloating, abdominal pain, excess wind, diarrhoea and constipation.

How long should the low FODMAP elimination phase last?

The elimination phase should last 2–6 weeks. Staying in elimination longer offers no extra benefit and can work against the gut microbiome, which thrives on fermentable fibres. If symptoms have not improved after six weeks, FODMAPs may not be the main trigger and other strategies should be explored.

Starting the low FODMAP diet: a dietitian's guide

Q: How does the low FODMAP diet work?

The low FODMAP diet is a three-step process: an elimination phase of 2–6 weeks where high FODMAP foods are swapped for low FODMAP alternatives, a reintroduction phase of 6–8 weeks where each FODMAP group is challenged one at a time to identify personal triggers, and an ongoing personalisation phase where only the foods that reliably cause symptoms are limited.

Q: Who should try the low FODMAP diet?

The low FODMAP diet is designed for people with a confirmed IBS diagnosis. Before starting, a GP should rule out other conditions with overlapping symptoms, such as coeliac disease. It is best undertaken with guidance from a dietitian to ensure proper nutrition and avoid unnecessary restriction.

Benjamin David
14 hours ago
3 min read

High and Low FODMAP fruits and vegetables

By Benjamin David APD

You may have heard about the low FODMAP diet from your GP or on the internet. It's the most researched dietary approach for irritable bowel syndrome (IBS), designed to help relieve symptoms of bloating and abdominal discomfort. It can help you identify which foods are problematic and which foods can reduce symptoms.

As a dietitian, it's one of the tools I use most often in clinic and one of the most misunderstood. Here's what you need to know before you start.

Key points

The low FODMAP diet is a short-term, highly restrictive plan used to decrease symptoms in people with IBS and help them identify which foods trigger symptoms.
FODMAPs are poorly absorbed sugars that can cause bloating, abdominal pain, wind, diarrhoea and constipation in sensitive individuals.
The diet follows a three-step process: eliminate high FODMAP foods, reintroduce them one by one, and then avoid only the foods that cause symptoms.
The diet is most helpful for people with IBS but should be done with guidance from a doctor or dietitian to ensure proper nutrition and avoid unintended weight loss.

What are FODMAPs?

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols, which are short-chain carbohydrates (sugars) that the small intestine absorbs poorly. Some people experience digestive distress after eating them. Symptoms include:

Abdominal bloating
Abdominal pain
Excess wind (flatulence)
Diarrhoea
Constipation

Importantly, FODMAPs are not unhealthy. Many high FODMAP foods are excellent sources of fibre and prebiotics, which is exactly why we don't restrict them any longer than necessary.

How does the low FODMAP diet work?

Line graph showing IBS symptoms dropping below the FODMAP symptom threshold during elimination, brief flares during reintroduction challenges, and well-managed symptoms during personalisation

The low FODMAP diet is a three-step process:

Elimination (2-6 weeks). Swap high FODMAP foods for low FODMAP alternatives to calm your symptoms down.
Reintroduction (6-8 weeks). Challenge each FODMAP group one at a time, in increasing amounts over three days, to identify your personal triggers.
Personalisation (ongoing). Bring back everything you tolerate and limit only the foods that reliably cause symptoms.

The key word to notice is swap, not remove.

Staying in elimination longer than six weeks offers no extra benefit and starts to work against your gut microbiome, which thrives on the very fermentable fibres you're restricting. If symptoms haven't improved after six weeks of doing the diet well, that's useful information too. It suggests FODMAPs aren't your main trigger and we can move on to other strategies rather than restricting unnecessarily.

The FODMAP diet is not a 'one size fits all' diet. Just because one person reacts to certain FODMAPs doesn't mean you will. That's why involving a dietitian in the personalisation and reintroduction phases is so important because the precision of identifying what actually works for you makes long-term eating flexible instead of fearful.

Who should try the low FODMAP diet?

The diet is designed for people with a confirmed IBS diagnosis. Before starting, your GP should rule out other conditions with overlapping symptoms such as coeliac disease.

How can a dietitian help?

While the low FODMAP diet may appear straightforward, it is considerably more complex to implement in practice. FODMAP content varies by portion size, ripeness, processing and even brand. Guidance through the reintroduction phase, using a structured and systematic approach, will give you clear answers.

Research consistently shows better symptom outcomes and better nutritional adequacy when the diet is guided by a dietitian trained in FODMAPs. A dietitian can also spot when the low FODMAP diet isn't the right tool for you in the first place and combine it with other strategies like fibre modification, meal pattern changes and gut-directed lifestyle support.

Ready to start with support?

Ben is an Accredited Practising Dietitian at Step Nutrition in Sandringham, helping people across Bayside Melbourne and Australia-wide via telehealth to manage IBS and gut health with evidence-based, practical support. If you'd like a structured, personalised plan for all three phases of the low FODMAP diet, book an appointment today.

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