In medicine, every new treatment tends to go through a cycle. First there is the breakthrough, the honeymoon phase, where it is miraculous, the answer to everything. Then comes the stage of disillusion as critical papers suggest that it may not be as good as was originally thought. Finally we arrive at a realistic appraisal, where the treatment becomes incorporated into the body of knowledge as a useful option for some people with particular symptoms and disease characteristics, but not for everybody.
The Honeymoon Phase
When papers on the low FODMAP diet first started to appear ten years ago, they captured the imagination of patients with IBS. Suddenly there was an explanation for symptoms of bloating and diarrhoea and a dietary treatment that seemed to work. In fact, the flatulent potential of onions and beans and the laxative action of certain fruits and, in some people, milk, had been known for many years and people with IBS had suspected that wheat might be problematic. But Professor Peter Gibson and his colleagues from Monash University, Melbourne, were the first to put it all together under a single concept, which they characterized by the acronym, FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols)1. These poorly absorbed sugars, which were present in milk, wheat, fruit and vegetables, either retained fluid in the bowel or released gas through fermentation, triggering symptoms of bloating, pain, diarrhea and flatulence in people with the sensitive guts of IBS.
Initial trials of a low FODMAP diet looked very good. As many as 75% of people with IBS benefitted from a diet that excluded or restricted FODMAPs, a figure that is similar to the first trials of high fibre diets for IBS and also the exclusion diets based on food specific IgG antibodies. The efficacy of the low FODMAP diet was supported in 2008 by a double blind food challenge of drinks containing fructose and fructans, which clearly demonstrated that symptoms of IBS returned when these FODMAPs were reintroduced into the diet2. It looked like the low FODMAP diet was here to stay for a while.
Have we reached The Stage of Disillusion?
FODMAPs, an important nutrient source for colonic bacteria, are essentially prebiotics, foods that nourish the colonic bacteria. So it was perhaps no surprise that a study from the Department of Dietetics and Nutrition at King’s College, London, published in 2012 revealed depletion of populations of bifidobacteria spp, a major component of the microbiome and a constituent of several probiotics3. This paper caused a more than a flutter of apprehension. Thoughout the noughties, paper after paper had appeared supporting the role of healthy populations of colonic bacteria in not only maintaining the integrity of the colon, and companies were falling over themselves to market probiotics, many of which contained bifidobacteria, yet here a treatment for IBS that appeared to deplete the microbiome and oppose their efforts. So could the short term gain caused by the low FODMAP diet cause longer term sensitivity and lock people into this dietary regimen, if not for life, for years? Trials of low FODMAP diets with probiotics are currently underway and early results suggest that the depletion of the microbome by reducing FODMAPs might be prevented if probiotics were prescribed concomitantly4.
So it is all beginning to get just a little confusing. Although there were a plethora of open studies supporting the benefits of the low FODMAP diet, most of them from the Monash and King’s groups, there were few long term studies on the efficacy of the combined exclusion/reintroduction protocol. Then last year, a survey was published from the King’s group, showing that 44% of patients achieved satisfactory relief of symptoms a year after starting low FODMAP exclusion/reintroduction, though 42% continued to avoid high FODMAP foods5, suggesting that they had not managed to complete the reintroduction protocol. Then a paper from Professor Marcus Simren’s Group in Gothenburg appeared comparing a low FODMAP diet with the kind of sensible diet that people with IBS were taking in Sweden before FODMAPs appeared6. There was no difference in the results though it has to be said that the sensible Swedish diet had also reduced onions and pulses. This compared with a previous study from the King’s group that showed that more patients improved while taking a low FODMAP diet compared with dietary advice issued in the NICE guidelines for IBS.
In my role of medical adviser to The IBS Network, I receive a lot of letters from people who have tried a low FODMAP diet. I have not attempted a survey of opinions, though specialist IBS dietitian Julie Thompson has recently posted a survey on The IBS Network website to gather that data. However my impression is that if people work through the reintroduction phase and discover which foods affect them, they can do well, though many others find it all too difficult and frustrating (see http://thedigestiondetective.com/blog-post/why-im-not-supportive-of-the-fodmap-approach.).
The risk that people might stay with the exclusion diet and become deficient of micronutrients such as calcium, iron or vitamins is of concern especially if they are vegetarian. There might also be a tendency to constipation caused by a reduction in fibre intake.
So have we now reached the stage of disillusion? Are people beginning to lose faith in the miracle of the low FODMAP diet? Could depletion of the microbiome caused by long-term adherence to a low FODMAP diet increase in intestinal sensitivity, permeability and activate the gut immune system, all of which could lead to perpetuation of IBS? Is reintroduction too difficult. Is it too controlled? Is there a lot more to managing IBS than diet? What about the sensitizing role of stress and emotional tension? (see ‘Reintroduction of FODMAPs. Is there an easier way?’ and ‘Why diets can fail’). There are still lots of questions to answer.
Towards a Realistic Appraisal
The FODMAPs concept has drawn attention to the range of foods in our diet that contain poorly absorbed simple and complex sugars that give rise to symptoms in people with IBS. Restricting the amounts of FODMAPs is therefore a useful first aid measure to reduce symptoms when the gut is particularly sensitive. Scientists are actively engaged on investigation of treatments to reduce visceral sensitivity, which, if realized, might render FODMAP restriction redundant. We are where we are. And for the moment, FODMAPs is a useful concept, that has increased understanding and improved management of IBS.
Any diet is only useful in the longer term if it is straightforward enough for patients to manage it themselves. It is unfortunate that the low FODMAP diet has been promoted by some as a regimen that can only be administered by specialist FODMAP-trained dietitians. The risks of nutritional deficiency could well be enhanced by overzealous adherence to the exclusion phase and the consequent difficulties in reintroduction.
Nonetheless, there will still be patients who are tortured by pain and bowel upset of IBS every day of their lives. Such suffering can make them quite desperate, but they may not just need the attentions of FODMAP trained dietitians, they might also require specialist psychotherapeutic intervention to desensitize the gut by calming the emotional centres in the brainstem.