The low FODMAP diet has become a popular treatment option for people living with IBS. But what are FODMAPs? What does the diet involve and how effective is it? Julie Thompson, a FODMAP trained registered dietitian and medical adviser to The IBS Network, explains.

What are FODMAPs?

FODMAP is an acronym that stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. They are a collection of poorly absorbed simple and complex sugars that are found in milk, wheat and some varieties of fruit and vegetable.

The FODMAPs are short-chain sugar molecules and some starchy long-chain ones (that are part of the fibre in our diet). They pull fluid from our body and then arrive in the large bowel where they are fermented by gut microbes. This, and the water that they absorb, causes the intestinal wall to stretch and expand. It’s like fermenting beer – the result is gas, bloating, and stretching a sensitive gut wall, which causes pain. For people with IBS who already have a highly sensitive gut, this ‘stretching’ causes heightened pain and discomfort.

What is the low FODMAP diet?

The low FODMAP diet is an exclusion diet that should only be carried out under the supervision of a registered dietitian trained in FODMAPs. The diet works by restricting FODMAP foods from the diet, before then reintroducing and identifying an individual’s trigger foods so a personalised diet plan can be developed. IBS is different for everyone and what works for one person may not work for another.

Background to the low FODMAP diet

The low FODMAP diet was developed in Australia in 2008, but its origins are older. At the time, gastroenterology dietitians were already aware of single food intolerances such as lactose, and that wheat, garlic, onion and mushrooms were particularly tricky for some people with digestive symptoms. Fructose intolerance (mainly found in fruit intolerance) was also known, but not as well-known as lactose intolerance, possibly because lactose is easier to identify as a problem by people with IBS.

The low FODMAP diet was novel in that the diet cut out all the possible high FODMAP foods in one go and then reintroduced them to individual tolerance, a breakthrough in treatment.

How effective is the low FODMAP diet?

The diet effectiveness varies — between five to eight out of 10 people see improvement. There is evidence stating that the diet helps up to 75% of IBS patients manage their symptoms better. This means therefore that 25% of IBS patients may not get relief of their symptoms via dietary changes and require other interventions to manage their symptoms.

The first stage of the diet

The first stage of the diet is reduction of high FODMAPs, which may then reduce IBS symptoms. Most symptoms improve within three to eight weeks. It is not a cure for IBS, and most people will still have a small degree of symptoms. Stage one is only the beginning.

The second stage of the diet

Stage two is learning about individual tolerances. This is a three-step re-introduction process that will show problematic foods. It may not be all of them.

Stage two is a vital part of the process. Fermentation in the large bowel is essential for good health and helps to provide fatty acids that keep the colon healthy. However, we know that the low FODMAP diet reduces the variety and numbers of microbes in the bowel. Our gut microbes are integral to us, and while it is possible to have some food for our microbiome (prebiotics) on the low FODMAP diet, the diet itself is the opposite of a prebiotic. It is, therefore, vital to re-introduce those high FODMAP foods that don’t give symptoms.

The third stage of the diet

The third stage of the diet includes following a FODMAP modified diet longer term, minimising symptoms and increasing diet variety. Once the foods causing symptoms have been identified people will have a list of tolerated foods and amounts that they can manage to eat without provoking symptoms. This makes the diet easier to follow and better nutritionally.

How easy is it to follow?

If the right support is provided a patient will be able to confidently follow the diet. NICE recommend that the low FOMAP diet ‘should only be given by a healthcare professional with expertise in dietary management’ (a dietitian).

A dietitian will personalise the advice to your situation and lifestyle. Planning is key to following the diet well and the dietitian can provide advice on checking ingredients lists, eating out and the availability of foods.

They also have the most up to date information about the FODMAP content of food, which has changed since the diet has been developed as more foods are tested. A lot of online information about the diet is incorrect or out of date. If people follow the diet online and find it’s not effective for them, this may be due to the incorrect information, not that the diet itself has been ineffective.

The low FODMAP diet should only be followed under the supervision of a registered dietitian.

More information is available on The IBS Network website here.