Foods falling into the FODMAP categories aren’t well absorbed in your small intestine, which is the main site for the absorption of all the macronutrients you need for energy and the micronutrients required for cell processes and optimal functioning. Therefore, these undigested components travel into your large intestine where they are attacked by the natural bacteria that live there and they undergo a process called fermentation. Gas is produced as a by-product of fermentation.
The actual strains of bacteria residing in your gut differ from person to person. Research has suggested that people with IBS may actually have markedly different strains of bacteria present compared to your average person. It is possible that ‘bad bacteria’ are more likely to trigger nasty symptoms as they carry out fermentation, such as producing excess gas, bloating, pain or a sudden change in bowel habits.
A second reason why FODMAPs may produce undesirable symptoms is that they are naturally osmotic. This means they pull water from the body into the intestine, which may explain why diarrhoea is often a symptom experienced with the consumption and processing of FODMAPs.
Lastly, there is some recent evidence to suggest that intestinal transport proteins such as GLUT5, which transports fructose in the small intestine, may not be working efficiently in people sensitive to FODMAPs. This would result in malabsorbed molecules of fructose being transported to undergo fermentation in the large intestine, which causes disruption in the colon environment.
Kassinen, A. et al (2007) The fecal microbiota of irritable bowel syndrome patients differs significantly from that of healthy subjects. Gastroenterology 133(1):24-33
Wilder-Smith, C.H. et al. (2014) Fructose transporters GLUT5 and GLUT2 expression in adult patients with fructose intolerance. United European Gastroenterol J. 2(1):14-21
If you are suffering from IBS or a functional gastrointestinal disorder, it is likely that FODMAPs are exacerbating your symptoms. Refer to our IBS symptoms page for an extensive and detailed list of symptoms linked with IBS.
The idea of following a low FODMAP diet in the treatment of IBS has been developed by researchers from the Monash University in Australia and it is estimated to produce favourable outcomes in up to 70% of IBS sufferers.
However, with IBS being such a multifactorial disorder, the solutions are not clear cut. It may be that you are not sensitive to all of the components of the FODMAP diet and/or cutting out many foods at once may actually have a detrimental effect on your gut bacteria or general health. You need to try to avoid losing out on the essential vitamins and minerals usually obtained from your diet that your body needs. Therefore nutritious alternatives are crucial at all stages of the FODMAP diet.
Please note that FODMAPs are often also very good sources of dietary fibre. Dietary fibre can be beneficial in people with diarrhoea - or constipation-dominant IBS but, in the case where you are sensitive to FODMAPs, it may be necessary to include FODMAP free dietary fibre in your diet. For more information, use the above.
In rare occasions people may be a sensitive to most sources of dietary fibre, either at the height of their problem or even longer term. In this case you may require a more complicated assessment by a medical professional.
So, you need to determine if the FODMAP diet produces favourable outcomes in terms of your IBS symptoms or not. Generally the FODMAP diet involves two main stages. The first stage involves cutting out all FODMAP foods, usually for a period of 6-8 weeks. In this time you should hopefully see a significant improvement in your symptoms.
After the initial stage of cutting out all FODMAP foods, the second stage is to try to reintroduce the different types of FODMAPs, one at a time, to determine which ones specifically cause a flare up of symptoms. Every case is individual but best case scenario is that some FODMAPs don’t produce symptoms and you are able to have as full and as varied a diet as possible.
Lactose intolerance is a good example of how it may not be the whole FODMAP spectrum causing you issues. Lactose intolerance is now fairly common. Lactose falls into the category of disaccharides, the ‘D’ in FODMAP. After the initial period of cutting all FODMAP foods from your diet, at the reintroduction stage you find only lactose products cause a flare up and all other categories are asymptomatic. This means you can still have a very healthy, varied diet and just simply restrict foods containing lactose. In contrast it could work the other way and lactose doesn’t cause you problems but certain fruit and vegetables do
It is very important to keep this in mind when considering using the FODMAP concept. We don’t want you to be restricting your diet unnecessarily.
As described here, the FODMAP diet isn’t always a straightforward solution and should be considered alongside the guidance of a medical professional such as a FODMAP trained dietician or nutritional therapist.