Why a low FODMAP diet may be the answer to your IBS

One study found that low-FODMAP diets reduced symptom severity in 76 percent of patients with IBS compared to a 54 percent reduction in a group receiving standard dietary advice. Bloating, flatulence, and abdominal pain were all reduced on the low-FODMAP diet.


FODMAPS are a collection of short-chain carbohydrates with chains of up to 10 sugars that vary in their digestibility and subsequent absorption. They are found in foods naturally or as food additives.

The acronym FODMAP stands for:

Fermentable – Capable of being fermented (by bacteria in the large intestine).

Oligosaccharides – Sugar molecules composed of 3 to 10 monosaccharide units.

Disaccharides – Sugar molecules composed of 2 monosaccharides. For example, milk sugar (lactose) is made from glucose and galactose whereas cane sugar is made from glucose and fructose.

Monosaccharides –Simple sugars consisting of 1 sugar unit. For example, glucose, fructose and galactose.


Polyols – Sugar alcohols (these carbohydrates don’t lead to intoxication!)


In a patient with healthy gut function, many of these carbohydrates are beneficial, acting as prebiotics that stimulate the proliferation of healthy gut microbes. In patients with digestive disorders, however, they can exacerbate symptoms like gas, bloating, diarrhoea, gut pain, and even GERD.

FODMAPs include:

FODMAPs are poorly absorbed in the small intestine and can pass undigested through to the large intestine where they are rapidly fermented by colonic bacteria. This process produces carbon dioxide, hydrogen, and/or methane gas, which can cause bloating, abdominal pain, flatulence, cramping and gurgling. The presence of short-chain carbohydrates in the large intestine also exerts an osmotic effect, increasing fluid movement into the intestinal lumen resulting in changes in bowel motion.

Low-FODMAP diets have been studied extensively for “functional gut disorders” like IBS. Consuming FODMAPs does not actually cause the gut disorder; rather, it exacerbates symptoms because it feeds the microbes in the small intestine. Thus, reducing FODMAPs may provide significant relief by reducing small intestinal bacterial overgrowth (SIBO). It is worth noting that about 84 percent of patients with IBS have a positive lactulose breath test for SIBO.

Unfortunately, no studies to date have looked at the effect of a low-FODMAP diet on long-term SIBO outcomes. Nevertheless, a low-FODMAP diet can provide effective short-term relief. One study found that low-FODMAP diets reduced symptom severity in 76 percent of patients with IBS compared to a 54 percent reduction in a group receiving standard dietary advice. Bloating, flatulence, and abdominal pain were all reduced on the low-FODMAP diet.

Because some FODMAPs have prebiotic effects, namely GOS and fructans, a low FODMAP diet reduces the intake of prebiotic fibres. Prebiotics are typically non-digestible fibre compounds that pass undigested through the upper part of the gastrointestinal tract and stimulate the growth or activity of advantageous bacteria that colonize the large intestine by acting as food for them.

A healthy balance of gut bacteria has several beneficial effects, especially in terms of improving digestion, enhancing mineral absorption, and strengthening the effectiveness the immune system.

Following a low FODMAP diet is very restrictive and it is therefore not something that should be implemented for life. However, cutting out foods high in fermentable carbohydrates for a period of four to six weeks can help a person regain control over their digestive symptoms and improve their quality of life. After the elimination phase is complete, foods can be “challenged” in the reintroduction phase, where FODMAPs are reintroduced one at a time with several days in between to monitor symptoms. Different people are sensitive to different FODMAPs, so it is important to identify which ones are the culprit.

Now that we’ve established why low-FODMAP is an appropriate choice for symptom relief, let’s look at what foods contain FODMAPs:

Excess fructose: honey, apple, mango, pear, watermelon, high-fructose corn syrup, agave syrup, dried fruit, fruit juice

Fructans: artichokes (globe), artichokes (Jerusalem), asparagus, beetroot, broccoli, Brussels sprouts, cabbage, eggplant, fennel, okra, chicory, dandelion leaves, garlic (in large amounts), leek, onion (brown, white, Spanish, onion powder), radicchio, lettuce, spring onion (white part), wheat, rye, pistachio, inulin, fructo-oligosaccharides.

Lactose: milk, ice cream, custard, dairy desserts, condensed and evaporated milk, milk powder, yogurt, soft unripened cheeses (such as ricotta, cottage, cream, and mascarpone cheese).

Galactans: legumes (such as baked beans, kidney beans, soybeans, lentils, chickpeas).

Polyols: apple, apricot, avocado, blackberry, cherry, longan, lychee, nectarine, pear, plum, prune, mushroom, sorbitol, mannitol, xylitol, maltitol, and isomalt.

I usually recommend removing all FODMAPs from the patient’s diet for a period of 30 days.

This may seem extreme, but in my clinical experience, most patients do not have the same reaction to each class of FODMAPs listed above. For example, some people seem to have no trouble with lactose but do very poorly with excess fructose. Others may tolerate polyols but not fructans. After the initial 30-day period, I recommend reintroducing FODMAPs one category at a time to see which are well tolerated. For instance, once the patient knows how fructans affect her, then you could recommend reintroducing the foods with excess fructose, and so forth.

It’s also rarely necessary to completely eradicate FODMAPs from the diet. FODMAP intolerance is not like gluten or casein intolerance. In those cases, the immune system reacts—regardless of how much of that food you eat. With FODMAP intolerance, it’s more of a threshold response. If a person is eating a lot of FODMAPs daily, the threshold for tolerating FODMAPs will be quite low. However, if the overall intake of FODMAPs is low, the patient may be able to tolerate small amounts without much problem.

Before embarking on a low-FODMAP diet, talk to a qualified health practitioner with experience in this field.