Low FODMAP Diet: What Is It and How Does It Work?

The low FODMAP diet is a short-term, three-phase eating plan that temporarily limits certain fermentable carbohydrates to see whether they trigger digestive symptoms such as bloating, wind and abdominal pain, mainly in people with irritable bowel syndrome (IBS). It is not a forever diet. The aim is to identify your personal triggers and then bring as many foods as possible back.

What does FODMAP actually mean?

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. These are short-chain carbohydrates found in a wide range of mostly plant-based foods. Your small intestine does not absorb them fully, so they travel on to the colon, where gut bacteria ferment them.

The main groups, with everyday examples, are:

Fructans and GOS (oligosaccharides): wheat bread and pasta, onion, garlic, chickpeas, broad beans and other pulses.
Lactose (disaccharide): milk, soft fresh cheeses, ricotta and yoghurt.
Excess fructose (monosaccharide): honey, apples, pears, mango and watermelon.
Polyols: mushrooms, cauliflower, stone fruits and some sugar-free sweeteners.

If you live in Malta, you will notice how many classics of Mediterranean cooking fall into these groups. Garlic and onion base a lot of sauces and stews, and pulses, bread and pasta are everyday staples. That does not make them unhealthy. It simply means they can be tricky for a sensitive gut.

How does it work?

Researchers at King’s College London used MRI to show that short-chain fermentable carbohydrates increase the water volume in the small intestine and the amount of gas produced in the colon. In people with visceral hypersensitivity, meaning a gut that is more sensitive to stretching, this can lead to pain, bloating and other symptoms (Staudacher and Whelan, 2017).

More recent work suggests the picture is wider than gas and water. A 2024 review describes possible roles for visceral hypersensitivity, intestinal permeability, changes in the microbiota, short-chain fatty acid production and gut motility, while noting that the exact mechanisms are still not fully understood (Bertin et al., 2024).

What does the evidence say?

The low FODMAP diet is recommended for IBS when general lifestyle and dietary advice has not been enough. A network meta-analysis of 13 randomised controlled trials looked at how it performs for global IBS symptoms and for individual ones such as pain, bloating and bowel habit (Black et al., 2022). A separate meta-analysis found that the diet reduced IBS severity by a moderate-to-large extent compared with a control diet (van Lanen et al., 2021).

A review of at least 10 randomised or randomised comparative trials reported a clinical response in 50% to 80% of people with IBS, particularly for bloating, flatulence, diarrhoea and overall symptoms (Staudacher and Whelan, 2017).

There are caveats worth knowing:

Much of the supporting evidence is of low quality, and most of it covers only the strict restriction phase (Bertin et al., 2024).
The diet changes the gut microbiota and metabolome, and how long those changes last and whether they matter clinically is not yet known (Staudacher and Whelan, 2017).
It does not work for everyone, and it is not a substitute for a medical diagnosis.

How do you start the low FODMAP diet?

Step 0: speak to your GP first

Bloating and bowel changes can have causes other than IBS, including coeliac disease and other conditions. A clinical protocol on the diet stresses a diagnostic evaluation, including any applicable tests, before starting (Lucas Zapata et al., 2024). See your GP if you have blood in your stools, unexplained weight loss, persistent or worsening pain, or symptoms that are new or different. Ideally, work with a registered dietitian, as cutting out many foods without guidance can make eating narrow and stressful.

Phase 1: elimination

You temporarily swap high-FODMAP foods for lower-FODMAP alternatives. One published protocol describes this phase as lasting two to three weeks (Lucas Zapata et al., 2024). Examples of easier swaps include:

Rice, oats, potatoes or gluten-free pasta in place of wheat-based staples.
Lactose-free milk or firm, aged cheeses instead of milk and fresh cheeses.
Oranges, strawberries or grapes instead of apples or watermelon.
Carrots, courgettes, tomatoes and spinach in place of onion-heavy or cauliflower dishes.
Herbs, spices and garlic-infused olive oil for flavour, since the fructans in garlic do not dissolve into the oil.

A food and symptom diary helps a lot. If you want to understand why healthy meals can still leave you uncomfortable, our article on feeling bloated after healthy meals is a good companion read.

Phase 2: reintroduction

This is the most important phase and the one most people skip. You reintroduce FODMAP groups one at a time, in a structured way, to see which ones you actually react to and in what amounts. The same protocol describes this stage as lasting around eight weeks (Lucas Zapata et al., 2024). Timing varies, so follow your dietitian’s plan rather than a fixed calendar.

Phase 3: personalisation

You build a long-term way of eating based on your own tolerance, including as many varied foods as you can. Many people find they only need to limit one or two groups, or just keep certain portions smaller.

Common mistakes to avoid

Staying in the elimination phase indefinitely. The diet is meant to be temporary, partly because of the microbiota changes seen in studies.
Cutting food groups without a reason. Start only if you have symptoms and, ideally, a diagnosis.
Ignoring other factors. Stress, sleep, meal size, eating speed and hydration all influence digestion. In Malta’s summer heat, drinking enough water matters too, especially if constipation is part of your picture. Our guide on digestive bloating and IBS covers these everyday factors in more depth.
Relying on apps and lists alone. FODMAP content depends on portion size, and lists change as research evolves.

Frequently asked questions

Is the low FODMAP diet a weight-loss diet?

No. It is designed to explore digestive symptoms, not to lose weight, and it should not be used for that purpose.

How long should I follow it?

Only the elimination phase is strict and short-term. It is then followed by reintroduction and personalisation. Your dietitian will guide the timing based on your symptoms.

Can I do it without a dietitian?

Some people try it alone, but support makes it safer and more effective, especially for reintroduction and for keeping your diet balanced. Speak to your GP first to rule out other causes of your symptoms.

Does everyone with bloating need the low FODMAP diet?

No. Bloating has many possible causes, and the diet has mainly been studied in people with IBS. If you have persistent symptoms, ask your GP or pharmacist for advice before changing your diet.

References

Gut & Glow is written by the team behind Brasil Botanique, a wellness brand being created for women in Malta. This article is for general information only and does not replace advice from your GP, pharmacist or dietitian.