11 Myths About IBS and FODMAPs: What Is Actually True?

The facts: The Rome Foundation, which sets the international criteria for IBS, classes it as a disorder of gut-brain interaction. Several factors are involved, in varying combinations: altered gut movement, an oversensitive gut, changes in the gut lining, immune system and gut bacteria, and changes in how the brain processes signals from the gut. Stress can make symptoms worse, and gut-directed hypnotherapy or cognitive behavioural therapy tailored to IBS can ease them. The fact that these treatments help does not mean the symptoms are imaginary, because they work on the connection between the gut and the brain. Read more in our IBS guide.

The facts: Your body makes IgG antibodies to foods as a perfectly normal response when you eat them regularly. A high level is therefore more likely to show what you have eaten often than what you do not tolerate. The European Academy of Allergy and Clinical Immunology (EAACI), the Swiss Society for Allergology and Immunology and the German IBS guideline advise against these tests, and the British guideline advises against exclusion diets based on IgG results. Instead, the German guideline relies on a food diary and a time-limited, targeted exclusion diet. Our article What are FODMAPs? explains how this works with FODMAPs in IBS.

The facts: Large population studies from Denmark, Taiwan and the UK found no higher long-term risk of bowel cancer in people with IBS, and the British guideline also states that IBS does not increase the risk of cancer. Bowel cancer was only more common shortly after diagnosis, in the Danish study mainly in the first three months. The researchers put this down to the fact that bowel cancer can cause similar symptoms at first and had initially been mistaken for IBS. Warning signs such as blood in your stool, unintentional weight loss or fever do not fit IBS, according to the guidelines, and the British guideline states that the usual bowel cancer screening still applies to people with IBS. You will find an overview of the warning signs in our IBS guide.

The facts: The FODMAP diet is about certain carbohydrates, whereas gluten is a protein. In the first phase, wheat, rye and barley are only limited because of their fructans, and small amounts are still allowed. According to Monash University, spelt sourdough bread, oats and soy sauce also fit in suitable portions, even though they contain gluten. Conversely, gluten-free products are not automatically low FODMAP: some contain onion, honey, or soy or lupin flour. With coeliac disease, the FODMAP diet is not enough, and if grains cause symptoms, the German guideline says coeliac disease and wheat allergy should be ruled out first. Read more in our article FODMAP vs gluten.

The facts: The FODMAP diet is a test in three steps. According to Monash University, the strict phase lasts 2 to 6 weeks, while the German guideline gives 6 to 8 weeks. After that, the FODMAP groups are tested one at a time, and in the long term only what causes symptoms is limited. Monash recommends retesting triggers later, because tolerance can improve, and points out that staying on a strict diet for a long time can reduce beneficial gut bacteria. Our articles What are FODMAPs? and FODMAP reintroduction test plan explain the process.

The facts: According to Monash University, studies from around the world show that 50 to 80 per cent of people with IBS respond to the diet. For everyone else, other treatments are an option, such as soluble fibre, medication or gut-directed hypnotherapy. The diet is meant for people whose IBS has been diagnosed by a doctor, not for losing weight. In people with an eating disorder, a strict diet can make disordered eating worse, which is why Monash advises health professionals to ask about this specifically before starting. Read more about the diet in our article What are FODMAPs?

The facts: Often it comes down to the amount. Monash University rates foods for a specific serving size, and its app shows the amount at which the traffic light changes from green to amber or red. One slice of wholemeal wheat bread, for example, is low FODMAP, but larger amounts are not, because of the fructans. With bananas, even ripeness counts: about a third of a ripe banana is low FODMAP, whereas a firm, medium-sized banana is low FODMAP even eaten whole. Read more in our articles on the Monash FODMAP app and FODMAP stacking.

The facts: Lactose is only one of six FODMAP groups. Fructans from wheat, onions and garlic, GOS from pulses, fructose and the sugar alcohols sorbitol and mannitol are also found in lactose-free food. According to Monash University, a dish without dairy can therefore still contain other FODMAPs. On the other hand, Monash says that only people who do not tolerate lactose well need to limit it, and even then usually not completely: most can manage 12 to 15 g a day, about the amount in 250 ml of milk. You can find out which groups cause you symptoms through reintroduction.

The facts: The effect depends on the bacterial strain, and medical societies take different views on probiotics. The German guideline (DGVS 2021) recommends selected probiotics, with the strain chosen according to symptoms. The British guideline (BSG 2021) considers that probiotics as a group may be effective, but cannot recommend a specific strain, and advises stopping them if there is no improvement after 12 weeks at most. The American guideline (ACG 2021) advises against probiotics for overall IBS symptoms. Our comparison of Kijimea Reizdarm PRO (sold in the UK as Kijimea IBS PRO) and FODZYME looks at one example.