(Updated 2019) by Lee Martin MSc RD
From time to time I get asked questions from journalists about the low FODMAP diet. I thought it would be useful to put some of these questions on the blog along with the answers I gave. You can also see the articles they went into here.
– Do you know how many people have a problem with digesting FODMAPS? Are there any statistics?
The problem is not from digesting FODMAPs but rather the symptoms experienced by those with IBS from malabsoprtion or bacterial digestion of FODMAPs. All FODMAPs will be absorbed differently by different people. There are no statistics for this although up to 20% of the world population may have IBS. Breath tests like the hydrogen breath test are often used to diagnose malbsorption of some FODMAPs like fructose. These breath tests however show poor reproducibility and and low predictive value for symptom responses therefore their use in IBS and functional bowel disorders is not routinely required. This was highlighted in a recent 2017 study by the Monash University research team and is open access (available here : Poor reproducibility of breath hydrogen testing: Implications for its application in functional bowel disorders)
– How does fructose malabsorption link with a general FODMAP ‘issue’ for people?
Fructose is only a problem when it is in excess of glucose within a food, or the food contains a high amount of added fructose. Most people will ‘malabsorb’ fructose if you give them enough fructose to eat. During the first part of the low FODMAP diet called the ‘restriction phase’, fructose is avoided along with the other FODMAPs. Due to fructose being absorbed with glucose there was a theory that adding glucose to food will enhance the fructose absorption. This was tested in a recent randomised control trial on people with fructose malabsorption which found adding glucose to fructose foods did not reduce any gastrointestinal symptoms. This paper is currently open access ( available here : Adding glucose to food and solutions to enhance fructose absorption is not effective in preventing fructose-induced functional gastrointestinal symptoms: randomised controlled trials in patients with fructose malabsorption)
See below for a great explanation of how fructose is absorbed in the body (taken from : Extending Our Knowledge of Fermentable, Short-Chain Carbohydrates for Managing Gastrointestinal Symptoms see here)
Fructose is absorbed in the small intestine via 2 pathways:
(1) high-capacity, facilitated transport using the GLUT2 transporter that absorbs fructose in the presence of glucose, and (2) low-capacity facultative transport that occurs via GLUT5. This latter pathway is downregulated in some individuals, giving rise to the potential for malabsorption of fructose. As such, fructose can still be ingested and absorbed in these individuals as long as glucose is present to prompt the GLUT2 pathway of absorption
– It looks as though there have been numerous studies on how FODMAPS relate to IBS. Is that right?
There are more studies coming out across the world all the time which is encouraging. Between 2018 and 2018 5 systematic review and meta-analysis were completed which can read here. The first of these studies identified 6 RCTs and 16 non-randomized interventions on the low FODMAP dietary treatment. The highlights from that study you can read in the abstract here. One of the best review of both the efficacy and mechanisms of the low FODMAP diet is by the FODMAP research team at King’s College London and can be read here.
– Any idea why some people and not others have this issue with FODMAPS?
What causes IBS is still being debated. In the past IBS was thought to be all in a person head! Over recent years the understanding of the pathophysiology of irritable bowel syndrome has increased. A review published in The Lancet (see here) discusses several potential underlying mechanisms behind IBS including; genetic factors (most notably an identified mutation of SCN5A); post-infectious changes, chronic infections and disturbances in the intestinal microbiota; low-grade mucosal inflammation, immune activation, and altered intestinal permeability; disordered bile salt metabolism (in 10–20% of cases with diarrhoea); abnormalities in serotonin metabolism; and gut–brain dysfunction. These factors are all difficult to study and there are many unknowns in the field of IBS.
– Any links to what exactly happens in the gut? Why people can’t digest FODMAPs properly?
Lactose requires lactase for digestion, fructose is absorbed via gut transporters, polyols are absorbed passively while humans lack enzymes to digest the oligosaccharides (FOS and GOS) which are digested for us by bacteria in our gut. Everyone will have different absorption capacities due to the different absorption processes just briefly mentioned. FODMAPs collectively all have the same effect on the gut; they increase the amount of water entering the large intestine and are subject to bacterial fermentation in the large intestine leading to symptoms of pain, bloating, wind, diarrhoea and even constipation. There is a nice figure explaining the mechanisms of how FODMAPs trigger gastrointestinal symptoms here.
– How long is it before people on the low FODMAP diet tend to see results?
For the vast majority roughly 4 weeks; with most people improving between 1-3 weeks. However it can take up to 8-12 weeks for some. Importantly if you do not see any change in symptoms after 4 weeks following the low FODMAP diet, or if your symptoms become worse during 4 weeks on the diet you should STOP. You should then start eating FODMAPs again as it is unlikely they are the main trigger of your symptoms. Go back to your medical professional to discuss further treatment option.
– Once people follow the terms of the low FODMAP diet, are they then able to relax the exclusions? i.e. does the gut heal and they can then tolerate FODMAPS? Or is the low FODMAP diet a life-time diet plan? I understand that the intolerance’s won’t be the same for all people.
The most important part of the low FODMAP diet is the reintroduction phase where you challenge high FODMAP foods systematically to assess your tolerance levels to the different FODMAPs. The low FODMAP diet should only be followed for a few weeks, preferably under the supervision of a registered dietitian. I think it is unfortunate that many people may follow a low FODMAP restriction diet for life because they have not sought the correct advice. The aim of the diet is to educate people to be able to self-manage their IBS symptoms allowing them to eat as much variety of foods as possible, including high FODMAP foods, but without eating too many foods that trigger symptoms. You will only find out the answer to this by completing the reintroduction phase and working out your personal tolerance levels. If you are thinking of reintroducing FODMAPs have a look at this article first. Work with a dietitian to achieve resolution of your FODMAP intolerance and if you cannot see a dietitian or want extra information then see more on how to challenge and reintroduce FODMAPs on www.reintroducingfodmaps.com
By the way not eating FODMAPs does not ‘heal’ the gut. FODMAPs do not damage the gut in any way.
– What other conditions is the low FODMAP diet useful for, apart from IBS?
The low FODMAP diet is an effective strategy for reducing symptoms of IBS. There may be applications for other conditions that have similar gastrointestinal symptoms such as Crohn’s disease, Ulcerative Colitis, Coeliac Disease or other functional bowel disorders although there is a lack of research for the effectiveness of the low FODMAP diet in these conditions at present.
– Are probiotics included in the low FODMAP diet plan?
A dietitian may consider probiotics as an option after a trail of the low FODMAP diet. The evidence suggests probiotics ‘may’ be beneficial for those with IBS however what probiotic you should take, for how long you should take it and who it will be effective in is unknown. Taking a probiotic is kind of like playing the lottery – there will be winners and losers.
– Presumably prebiotics aren’t included? This goes against many of the other ‘gut soothing’ diets that are around.
For those who experience symptoms from eating food containing FODMAPs a ‘gut soothing’ diet containing prebiotics such as FOS (fructooligosaccharides) or GOS (galacto-oligosaccharides) which are both FODMAPs will probably increase rather than decrease their symptoms. However prebiotics are an important part of the diet and research has shown they can be beneficial for gut health. This is another reason why the low FODMAP diet should only be used for a short period and preferably under the guidance of a qualified dietitian trained or experienced in the low FODMAP diet.
Here is a link to some of the full media articles relating to these questions and many more. They are all good articles based on the research behind the diet so worth a read.
Good news! The first ever book dedicated to reintroducing FODMAPs is now available to purchase on Amazon. The book is titled ‘Re-challenging and Reintroducing FODMAPs – A self-help guide to the entire reintroduction phase of the low FODMAP diet’. Click below for more details.
Looking for The Best Low FODMAP Diet Resources, click here.
Dietitian authored articles on the FODMAP dietary treatment available here.
For dietitian approved low FODMAP recipes see here.
We recently travelled around the world and blogged about following a modified FODMAP diet. See more on our FODMAP blog Travel section.