Low FODMAP diet explainer: what does the evidence say?

In Eat well, Nutrition education by RebeccaLeave a Comment

No idea what ‘FODMAPs’ are? Don’t worry, you’re not behind the times – it’s a relatively new concept in nutrition.

FODMAPs stands for: Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols.

In simple terms, FODMAPs are a particular group of carbohydrates that are digested (or not digested) in similar ways. So what’s the Low FODMAP Diet used for, and should you try it?

What’s the premise of the Low FODMAP Diet?

FODMAPs are a group of carbohydrates that are either poorly absorbed in the small intestine or are completely indigestible. Malabsorption of FODMAPs is normal, and for many people this doesn’t cause any problems. But for those with Irritable Bowel Syndrome (IBS) certain FODMAPs can cause great discomfort. Symptoms of IBS include bloating, cramping, pain, alternating diarrhoea and constipation, and nausea.

The diet has three phases:

  1. Elimination: completely avoiding all FODMAP foods for 4-6 weeks or until you’re free of IBS symptoms
  2. Challenge: reintroducing FODMAP foods in a specific order to determine your triggers and thresholds
  3. Adaptation: reintroducing non-trigger foods to give the most dietary variety as possible, while continuing to avoid IBS trigger foods

What’s true?

The Low FODMAP Diet was created and refined through scientific research [1]. Once you’re diagnosed with IBS by your GP, undertaking the Low FODMAP Diet can help you identify trigger foods and find a diet that suits your body.

Food intolerances are all about quantity – how much can someone tolerate before they experience symptoms. When people who are sensitive to particular foods exceed their body’s threshold to tolerate that food, gastrointestinal symptoms appear. The Low FODMAP Diet helps people to determine what foods are triggering their symptoms and how much of those particular foods they can tolerate.

Since its inception in the mid-2000s, the Low FODMAP Diet has become a leading management therapy for Irritable Bowel Syndrome (IBS) triggered by food intolerances [2].

 FODMAP Food type Food sources
OligosaccharidesFructansWheat (white bread, pasta, pastries, cookies), rye, onions, artichokes, asparagus, beetroot and leek.
GalactansLegume beans (eg. baked beans, kidney beans) lentils, chickpeas, cabbage and Brussels sprouts.
DisaccharideLactose (milk sugar)Milk, ice cream, custard, dairy desserts, condensed and evaporated milk, milk powder, yoghurt, margarine, soft unripened cheeses (e.g. Cottage, ricotta, cream).
MonosaccharideFructose (fruit sugar)Honey, apples, mango, pear, watermelon, peaches, dried fruits (e.g. prunes, figs, dates and raisins), and high fructose corn syrup.
PolyolsSugar PolyolsApples, apricots, avocado, cherries, lychee, nectarines, pears, plums, prunes, mushrooms, sorbitol (420), mannitol (421), xylitol (967), maltitol (965) and isomalt (953).

What’s false?

Some people see the Low FODMAP Diet as a long-term eating pattern for weight loss or general wellness. This is not the case.

A strict Low FODMAP Diet is a time-limited process [3]. It is not suitable for everyone. Due to the restrictiveness of the diet, it is best if the Low FODMAP Diet is supervised by a dietitian. This will help to ensure your individual nutritional needs are being met and you’re not going to inadvertently face other health concerns such as an imbalance of gut bacteria, or disordered views of food and eating. [4]

Once you’ve been through the elimination/challenge cycle, it’s important to adapt your regular diet to include as many healthy foods as you can at appropriate quantities. This will ensure you’re not missing out on other vital nutrients that are also found in the foods you can’t tolerate. You can repeat the elimination/challenge process for foods that you still aren’t tolerating well to see if you can consume them in different quantities or to really pinpoint your triggers.

It’s important not to restrict foods in the long-term, particularly if they don’t give you IBS symptoms

What does the evidence say?

The Practice-based Evidence and Nutrition (PEN) summary of evidence says that:

  • Data from several short-term controlled clinical trials suggests that a low FODMAP diet can reduce gastrointestinal symptoms, compared to no dietary intervention in up to 75% of individuals with IBS.
  • A low FODMAP diet has only been evaluated as a dietitian-delivered intervention for about six to eight weeks.
  • The risk of nutritional inadequacy is a concern, particularly if the diet is self-selected or followed long term.
  • Additional studies are needed to establish the long-term effectiveness of the diet, to examine the impact on gut microbiota, and to identify predictors that will help select individuals likely to respond to this treatment.

If you have been diagnosed with IBS and want to identify trigger foods, a dietitian can support you through the Low FODMAP Diet and help you achieve a nutritionally adequate, enjoyable, and long-term diet.


[1] Discover the research behind the Low FODMAP Diet – Monash University [2] Gibson P. History of the low FODMAP diet. Journal of Gastroenterology and Hepatology 2017; 32 (Suppl. 1): 5–7 [3] Starting the Low FODMAP Diet – Monash University [4] Hill P, Muir J, Gibson P. Controversies and Recent Developments of the Low-FODMAP Diet. Gastroenterol Hepatol (N Y). 2017 Jan; 13(1): 36–45.