Nutrition > Diets

Low FODMAP diet for irritable bowel syndrome

Dr. med. Andre Sommer

Dr. med. Andre Sommer

FODMAPs are substances that are naturally found in many foods. These substances are not harmful. However, it is believed that in many people with irritable bowel syndrome their body is sensitive to them. This is also referred to as FODMAP sensitivity. A low-FODMAP diet can therefore provide relief for irritable bowel syndrome. The goal is not to live completely FODMAP-free. Rather, you can try to consciously reduce the amount of FODMAPs.

What are FODMAPs?

The word FODMAP stands for** fermentable **oligosaccharides, disaccharides, monosaccharides and polyols. Saccharide stands for sugar, which is the basic substance of these substances. FODMAPs are certain short-chain sugars (carbohydrates) and sugar alcohols.

FODMAPs are fermentable carbohydrates. If FODMAPs are poorly absorbed in the small intestine (malabsorption), they reach the large intestine. Fermentation processes can occur during the digestion of FODMAPs. This process is called fermentation. Bacteria in the colon decompose the FODMAPs. There are hardly any bacteria in the small intestine. If the small intestine is colonized incorrectly, FODMAPs are also metabolized here.

How are FODMAPs digested?

The fermentation of the FODMAPs releases nutrient salts (electrolytes) and water, among other things. In addition, gases such as methane and carbon dioxide (CO2) and hydrogen (H2) are released. In addition to these gases, short-chain fatty acids are formed during fermentation. These include propionic acid (metacetonic acid) and butyric acid.

FODMAPs are rarely problematic for a healthy intestine. However, a FODMAP diet can be useful for a hypersensitive intestine, since the resulting gases can also irritate.

Why are FODMAPs poorly absorbed in the gut?

There are various reasons why FODMAPs are poorly absorbed (absorbed) in the intestine. The main reasons include:

  • Channels and transporters for the intake of sugar are overwhelmed with the intake of the sugar (for example, in the case of fructose intolerance) or there are no suitable transporters for a particular sugar
  • Sugar alcohols are too large to pass through the intestinal wall
  • Enzymes for the breakdown of certain sugars (e.g. galactans) are missing in the intestinal wall
  • Enzymes (especially lactase) cannot cope with the sugar breakdown

How do FODMAPs cause bowel problems?

FODMAPs can lead to bloating of the intestine, as more water flows into the intestine through the substances (osmotic effectiveness). In addition, more gas is produced. Increased gas production by FODMAPs has also been found in people with irritable bowel syndrome using hydrogen breath gas tests (H2Breath tests).

This results in a bloated stomach, bloating and loss of air (flatulence) as well as a changed movement of the intestine (intestinal motility) and pain. The expansion of the intestinal wall also makes it more permeable, which increases the likelihood of inflammation (increase in intestinal permeability). How exactly FODMAPs influence the intestinal flora of humans positively or negatively has not yet been sufficiently clarified.

Why do people with irritable bowel tolerate FODMAPs less well?

Although FODMAPs are digested poorly by everyone, they are not inherently bad. However, people affected by intestinal diseases such as irritable bowel syndrome react particularly strongly to FODMAP-rich food for various reasons:

  • Visceral hypersensitivity: With irritable bowel syndrome, the intestines are hypersensitive so the effects of FODMAPs are perceived as worse.
  • Microbiome: Irritable bowel syndrome leads to a change in the bacterial colonization (intestinal flora), which is accompanied by an altered fermentation of the FODMAPs.
  • Motility disorder: Changed activity of the intestinal muscles and the nervous system of the intestine in irritable bowel syndrome leads to an increased tendency of the intestinal muscles to cramp under the influence of FODMAPs.

Studies have shown that a low FODMAP diet has a positive effect in around 60 to 70 percent of constipation-type irritable bowel syndrome patients. It is still unclear which mechanisms lead to the improvements.

How does a low FODMAP diet work?

A low FODMAP diet consists of two phases. At the beginning there is the restriction phase (also known as the elimination phase), in which FODMAPS are avoided as far as possible. In the second phase, there is a gradual re-exposure, in which various foods containing FODMAP are slowly reintroduced into the diet. The second phase of the low-FODMAP diet is demanding but important.

  1. **Restriction phase: **Foods rich in FODMAPs are not consumed for six to eight weeks. There is also evidence that avoiding gluten can also be helpful.
  2. **Re-exposure: **During the step-by-step re-exposure, certain foods rich in FODMAP are successively re-added to the menu. You also keep a diary of the symptoms. The aim of the re-exposure is to determine the individual tolerance limit for FODMAP and gluten-rich foods. An individual nutritional plan can also be worked out in this way. This is often more balanced than a strictly combined gluten-free and low-FODMAP diet. In the re-exposure phase, food can be added every week. This food can be consumed in a normal serving at least twice during the test week.


One should have realistic expectations of the diet and be aware that despite a change in diet, symptoms can still occur. Not everyone can be free of complaints. Nevertheless, the low-FODMAP diet is currently a relevant treatment alternative for irritable bowel syndrome.

Which oligosaccharides belong to the FODMAPs?

The fact that we experience increased bloating after eating legumes is due to the oligosaccharides. Oligosaccharides are carbohydrate chains that consist of three to nine simple sugars (monosaccharides). Oligosaccharides include fructans, galactans, fructo-oligosaccharides and galacto-oligosaccharides.

  • **Vegetables **that contain FODMAPs in the form of fructans include artichokes, broccoli, peas, fennel, garlic, cabbage, leek, Brussels sprouts, arugula, asparagus and onions.
  • **Grains **that contain FODMAPs in the form of fructans include rye, wheat and barley.
  • **Fruits **that contain FODMAPs in the form of fructans include persimmons, nectarines, white peaches and watermelons.
  • Legumes that contain FODMAPS in the form of galactans include red and white beans, chickpeas and lentils. The saying that beans make you “toot” describes the effect of FODMAPs on gas production and fermentation processes during digestion, because legumes are particularly rich in oligosaccharides.


Which disaccharides belong to the FODMAPs?

Disaccharides are double sugars. Milk sugar (lactose) is a disaccharide FODMAP. Lactose consists of the simple sugars glucose and galactose. For example, the sugar is found in lactose-containing milk, yogurt, ricotta and cottage cheese. Lactose is broken down by the enzyme lactase in the intestinal mucosa and then taken up. If there is not enough lactase, there are typical symptoms of FODMAP intolerance such as gas development, bloating and abdominal pain.

It is now believed that there are different levels of lactose intolerance. In addition to people who tolerate lactose (lactose tolerance) and people who do not tolerate lactose (lactose intolerance), intermediate forms are also suspected. Lactose tolerance changes depending on lifestyle and age: While almost all infants tolerate lactose, the majority of adults worldwide are lactose intolerant. This would also explain why FODMAP tolerance deteriorates in some cases throughout life.

Which monosaccharides belong to the FODMAPs?

Monosaccharides are simple sugars. Among the simple sugars, fructose is one of the FODMAPs. Fructose is used as a sweetener in soft drinks and many other foods. In the past few years, corn syrup (also called high-fructose corn syrup, HFCS) has increased the consumption of fructose significantly. In addition, fructose is a FODMAP found in fruits such as apples, pears, figs, mangoes, canned fruits, dried fruits and watermelons. Artichokes and asparagus also contain the FODMAP fructose. Honey also has a high fructose content.

Fructose is mainly absorbed in the small intestine by a specific transporter (GLUT-5). In patients without irritable bowel syndrome or fructose intolerance, the fructose transporters' capacity to absorb is limited. If too much fructose is taken in at once, some of the FODMAPs remain in the intestine and the typical symptoms of FODMAP intolerance occur.

Experiments show that 80 percent of healthy people suffer from poor absorption (malabsorption) with an amount of 50 grams or more of fructose. Fructose intake can be improved by taking glucose at the same time. GLUT-2 transporters play an important role here. If glucose and fructose are consumed together, the relationship between the two sugars is important. For example, half a banana is allowed on a low-FODMAP diet. Household sugar (sucrose) can also be eaten in very small quantities. However, if there is an excess of fructose, this can lead to symptoms.

Why do sugar substitutes cause diarrhea?

Polyols are sugar alcohols, the well-known representatives of which are sorbitol (sorbitol), mannitol (mannitol), xylitol (xylitol) and maltitol (maltitol). Polyols are found in some types of fruit and vegetables. For example, apples, apricots and cherries contain polyols. If children snack on too many cherries and don't feel well, for example, this is a result of the bacterial fermentation of the FODMAPs contained in cherries.

However, polyols are also often used as sugar substitutes in low-calorie foods. Polyols are also added in sugar-free sweets and chewing gums in order to protect the teeth.

FODMAPs are osmotically effective. This means that they bind fluid or even pull it out of the intestine into the stool. This can lead to diarrhea if the intake is high. Since they are poorly absorbed through the intestinal wall and attract water, they liquefy the stool. This phenomenon is clear from the warning: “Can have a laxative effect if consumed to excess”.

EU Directive 94/35 / EC obliges manufacturers to label the following FODMAPs (polyols) that are used as sweeteners:

  • Sorbitol (E 420)
  • Mannitol (E 421)
  • Isomalt (E 953)
  • Maltitol (E 965)
  • Maltitol syrup (E 965)
  • Lactite (E 966)
  • Xylitol (E 967)
  • Erythritol (E 968)

Can anyone try the low-FODMAP diet?

FODMAPs serve as food for the bacteria in the intestine. So the bacteria are deprived of the nutritional basis by a diet low in FODMAPs. Therefore, especially people with a healthy intestinal flora should carefully consider whether they want to change the composition of the bacteria (microbiome) through a low FODMAP diet. The exact influence of the low FODMAP diet on the microbiome has not yet been sufficiently researched. In particular, the long-term consequences of the diet are not yet known.

There is evidence that a low-FODMAP diet can also inhibit the growth of positive bacteria and make the stool more alkaline (increase in pH). For example, bifidobacteria, ruminococcus gnavus, akkermansia muciniphila and _lactobacilli _can be disturbed in growth. This can have negative consequences for intestinal health.

For this reason, those affected by irritable bowel syndrome should only carry out the diet together with other therapy components and only for a limited time (about two months). Symptoms often improve during this period. After eight weeks, certain FODMAP-rich foods can be included in the diet again.

A low-FODMAP diet should be discussed with the attending doctor beforehand. The reason is that with some other diseases such as diabetes mellitus, such a massive intervention in the sugar balance has to be carefully considered and closely monitored.

How is the FODMAP content of food determined?

The FODMAP diet has become known through Australian researchers. Hence the measurement methods come from Australia. To measure the FODMAP content in food, high-performance liquid chromatography (HPLC) is used in conjunction with light scattering detectors (Evaporative Light Scattering Detector, ELSD). This technique allows the amount of fermentable carbohydrates (FODMAPs) in food to be determined.

There are various books and websites that provide recipes with low-FODMAP foods for people on the diet.

Does the low-FODMAP diet affect histamine metabolism?

A study from March 2016 showed that the low-FODMAP diet reduces histamine levels in the blood and urine. In the comparison group with high FODMAP intake, the histamine levels were comparatively increased. The researchers suspect that histamine plays an important role as a signaling molecule in the development of irritable bowel symptoms. However, results of individual, small studies should always be enjoyed with caution. Only findings that can be confirmed in several large studies are really reliable.

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Dr. med. Andre Sommer

Dr. med. Andre Sommer

I’m André, a medical doctor from Berlin. Together with a team of medical doctors, nutritionists and data scientists we empower people to understand digestive issues with our app Cara.

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