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The research behind the low FODMAP diet

The research behind the low FODMAP diet

by FoodMaestro | 23 June 2016

The research behind the low FODMAP diet -  By Dr Megan Rossi 

These days we’re constantly bombarded with new diets, each one claiming to work miracles, to help us achieve healthier and happier lives, but how do we know which ones are actually worth trying and which ones should be thrown out with the trash?

Just like you wouldn’t buy a house without researching the market, you shouldn’t try a new diet without researching the evidence. I know it sounds really rather boring, trust me I do however researching the effectiveness of a diet (rather than blindly following the newest and shiniest new fad diet) is a must do to ensure that we:

1) Don’t waste time or money; & that

2) It’s safe- yes believe it or not, eating the wrong thing can be risky business. In fact, poor diet is one of the leading causes of chronic disease.

SO you ask, what about the Low FODMAP diet? How does it stack up against the research?

The low FODMAP diet has been strenuously put through its paces by top researchers from around the world, with close to 30 clinical trials investigating whether or not the diet works. Although these numbers sound impressive, unfortunately for us it’s not that straightforward and attention to the trial details is critically important. As the old saying goes “all men are created equal” but unfortunately this does not ring true with clinical trials and the quality and therefore the validity of findings can be highly variable. For example, some studies include only a small number of participants who may be very different to the general IBS cohort, making it difficult to extrapolate the findings to the larger population.  Another limitation, particularly in diet-based research, is the difficulty of blinding participants to their intervention, meaning the participants know which group they've been allocated. This can subconsciously effect their response to treatment, a phenomenon known as the ‘placebo effect’.  KEY MESSAGE: Not all research is equal!

Thankfully, determining the quality of the evidence can be left to the experts who are trained in techniques that involve pooling together all of these individual studies, assessing their risk of bias, and then estimating the intervention’s overall effectiveness (you may have heard researchers refer to this as a systematic review or meta-analysis). This process has been undertaken for the low FODMAP diet in IBS1, and concluded when delivered by a dietitian the low FODMAP diet improved:

1)     Overall symptoms* (in up to 70% of people)

2)     Abdominal pain*

3)     Bloating*

4)     Quality of life*

5)     Flatulence

6)     Bowel habit (both diarrhea and constipation)

Note: * strongest evidence

In fact, the evidence has been so convincing that national bodies including the British Dietitian Association2 (hot off the press!!) and the National Institute for Health and Care Excellence3 have incorporated the low FODMAP diet in their evidence-based guidelines for the management of IBS.

But how do we know it’s the FODMAPs and not other components of food? (I hear the skeptics say)

Food is incredibly complex. In fact, researchers are constantly finding new compounds that can cause gastrointestinal distress in sensitive people. Nonetheless, in the FODMAP space there has been considerable research linking the individual FODMAPs to symptoms. These mechanisms have been explored in a number of ways. A research group from the UK have used an advanced imaging technique (known as MRI) to visually demonstrated that compared to glucose, isolated FODMAPs increase more fluid and greater gas volumes in the intestine.4 Other studies have also challenged participants with isolated FODMAPs compared to glucose in a randomized, blinded manner and showed a dose dependent increase in IBS symptoms with increasing FODMAP load.5 Convinced yet?

So the diet works (for most) and we understand the mechanisms (at least most), BUT is it safe?

The question of safety is often overlooked by many (fad) diets, which, although in the short term maybe associated with benefit, can actually lead to poor health outcomes (*cough* carb-free diet *cough*). The safety of the low FODMAP has been explored; and although considered safe in the short term, there were two main areas for concern. First, the diet alters the gut microbiota (the technical term for the trillions of gut bacteria that live in our gut) which maybe important in long term symptom management; and second, stage 1 of the diet reduces calcium intakes. These findings reinforce the importance of reintroducing individual FODMAPs to personal tolerance through dietitian-delivered systematic food challenges ie. Stage 2 of the low FODMAP diet discussed in my previous blog. A step-by-step guide on how to reintroduce is also one of the great features of the low FoodMaestro FODMAP app. 

Take home messages (for those I may have lost along the way):

1. The low FODMAP diet has been shown to be effective in managing IBS symptoms in up to 70% of people

2. There is clear mechanistic rationale, strengthening the scientific merit of the diet

3. The diet is safe to follow in the short term, although reintroducing individual FODMAPs is important to ensure the long-term safety.

Related articles by Dr Megan Rossi in the irritable bowel syndrome (IBS) series:

  1. Introduction to a low FODMAP diet - By Dr Megan Rossi 
  2. The research behind the low FODMAP diet -  By Dr Megan Rossi 
  3. Lactose guidelines for the FODMAP diet by Dr Megan Rossi
  4. Beyond the low FODMAP diet By Dr Megan Rossi
  5. Why the low FODMAP diet may not be working for you

By Dr Megan Rossi 

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Twitter: @DrMegan_RD


1. Marsh, A, Eslick, EM, Eslick, GD: Does a diet low in FODMAPs reduce symptoms associated with functional gastrointestinal disorders? A comprehensive systematic review and meta-analysis. Eur J Nutr, 55: 897-906, 2016.

2. McKenzie, YA, Bowyer, RK, Leach, H, et al.: British Dietetic Association systematic review and evidence-based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update). J Hum Nutr Diet, 2016.

3. National Institute for Clinical Excellence: Irritable bowel syndrome in adults: diagnosis and management of irritable bowel syndrome London, National Institute for Clinical Excellence, 2015.

4. Murray, K, Wilkinson-Smith, V, Hoad, C, et al.: Differential effects of FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols) on small and large intestinal contents in healthy subjects shown by MRI. Am J Gastroenterol, 109: 110-9, 2014.

5. Shepherd, SJ, Parker, FC, Muir, JG, et al.: Dietary triggers of abdominal symptoms in patients with irritable bowel syndrome: randomized placebo-controlled evidence. Clin Gastroenterol Hepatol, 6: 765-71, 2008.