Nutrition > Diets

FODMAPs: The Essential Guide to the Low-FODMAP diet for IBS

Dr. Sarah Toler, CNM, DNP

Dr. Sarah Toler, CNM, DNP

FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) are substances that are naturally found in many foods. These substances are not harmful to most people. It is believed many people with irritable bowel syndrome are sensitive to some or all of these compounds.

This is also referred to as FODMAP sensitivity. A low-FODMAP diet may provide relief from irritable bowel syndrome. Most people with IBS do not completely remove all FODMAPs from their diets. Most consciously reduce the amount of FODMAPs or eliminate FODMAP foods one-by-one to find which cause IBS flare ups.

What are FODMAPs?

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

FODMAPs are rarely problematic for a healthy intestine. If FODMAPs are poorly absorbed in the small intestine, also called malabsorption, they attract water. The result is pain, bloating, flatulence, and diarrhea.

A low FODMAP diet can be useful for a hypersensitive intestine, since the resulting gases caused by FODMAPs can be irritants.

How do FODMAPs cause bowel symptoms?

Fermentation processes can occur during the digestion of FODMAPs. Bacteria in the colon decompose the FODMAPs. If the small intestine microbiota is imbalanced, FODMAPs are also metabolized here.

FODMAPs can lead to bloating of the intestine, as more water is pulled into the intestine, drawn to the substances osmotically. This process produces more gas in the intestine. Increased gas production by FODMAPs has been found in people with irritable bowel syndrome using hydrogen breath gas tests.

This results in bloating, flatulence, as well as changes in intestinal motility, and pain. The expansion of the intestinal wall also makes it more permeable, which increases the likelihood of inflammation. How exactly FODMAPs influence the intestinal flora of humans positively or negatively is not well understood.

Foods with FODMAPS

Which oligosaccharides are FODMAPs?

Have you ever noticed bloating or flatulence after eating a bowl of beans? Increased bloating after eating legumes is due to the _oligosaccharide _content.

Oligosaccharides are carbohydrate chains that consist of three to nine simple sugars called monosaccharides.

  • Vegetable that contain FODMAPs include artichokes, broccoli, peas, fennel, garlic, cabbage, leek, Brussels sprouts, arugula, asparagus, and onions.
  • Grains that contain FODMAPs include rye and wheat.
  • Fruits that contain FODMAPs include persimmons, white peaches, apples, and watermelons.
  • Legumes that contain FODMAPS include red and white beans, chickpeas, and lentils. The flatulence that often follows a meal rich in beans is produced by the effect of FODMAPs on gas production and fermentation processes during digestion, because legumes are particularly rich in oligosaccharides.
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Which disaccharides are FODMAPs?

Disaccharides are double sugars. Milk sugar, called lactose, is the disaccharide in FODMAP. Lactose is broken down by the enzyme lactase in the intestinal mucosa, and then absorbed. If there is not enough lactase, there are typical symptoms of FODMAP intolerance like gas, bloating, and abdominal pain.

It is now believed that there are different levels of lactose intolerance. In addition to people who tolerate lactose and people who do not tolerate lactose, it may be possible to have intermediate levels of lactose intolerance. 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 are FODMAPs?

Monosaccharides are simple sugars. Among 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, or HFCS, has increased the consumption of fructose significantly.

Fructose is a FODMAP found in:

  • apples
  • pears
  • watermelons
  • mangoes
  • canned and dried fruits
  • honey
  • soft drinks
  • food containing corn syrup (also called high-fructose corn syrup, or HFCS)

In all people, even those without irritable bowel syndrome or fructose intolerance, the capacity to absorb is limited because the human gastrointestinal system was designed to only intake small amounts of fruit, and not the large amounts of sugar many diets include today.

If too much fructose is ingested at once, some of the FODMAPs remain in the intestine and the typical symptoms of FODMAP intolerance occur. Some research has indicated that 80 percent of people who eat 50 grams or more of fructose per day do not absorb it well.

Which polyols are FODMAPS? And why do sugar substitutes cause diarrhea?

Polyols are sugar alcohols, the well-known representatives of which are sorbitol, mannitol, xylitol, and maltitol.

Polyols are found in some types of fruit and vegetables:

  • Apples
  • Apricots
  • Cherries

If children snack on too many cherries and don't feel well, this is a result of the bacterial fermentation of the FODMAPs contained in cherries.

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 from cavity-causing sucrose.

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 with high intake. Since they are poorly absorbed through the intestinal wall and attract water, they liquefy the stool.

The United States Food & Drug Administration (FDA) labels certain polyol FODMAPs as food additives with specific requirements. These FODMAPS are used as sweeteners and are required to have the following statement on the label of the food product: "Excess consumption may have a laxative effect."

  • Sorbitol
  • Mannitol

How do people with IBS digest FODMAPs?

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

  • Visceral hypersensitivity: With IBS, the intestines are hypersensitive, so the effects of FODMAPs may be more intense.
  • Microbiome: IBS leads to a change in the intestinal flora, which may alter the fermentation of the FODMAPs.
  • Motility disorder: In some cases of IBS, changed activity of the intestinal muscles and the nervous system of the intestine leads to either increased cramping or increased constipation after eating FODMAPs.

How does a low FODMAP diet work?

A low FODMAP diet consists of two phases. At the beginning there is an elimination phase, during which FODMAPS are avoided as much as possible.

In the second phase, there is a gradual re-exposure, in which foods containing FODMAP are slowly reintroduced. The second phase of the low-FODMAP diet is demanding, but important.

  1. Elimination phase: Foods rich in FODMAPs are not consumed for 2-6 weeks. There is evidence that avoiding gluten can also be helpful.
  2. Re-exposure: During the step-by-step re-exposure, certain foods rich in FODMAPs are successively re-added to the menu, while keeping a diary of symptoms.

The aim of re-exposure is to determine the individual tolerance limit for FODMAP and gluten-rich foods. An individual nutrition plan can be developed this way. This is often more balanced than a strictly combined gluten-free and low-FODMAP diet. The re-exposure phase usually lasts 6 to 8 weeks.


Important

Realistic expectations of the diet are helpful, as is an awareness that despite a change in diet, symptoms can still occur. Some people find that symptoms are greatly reduced with an elimination diet, although not reduced completely.

Any elimination diet should be followed with a nutritionist who can help with vitamin and mineral supplementation where needed.


Can anyone try the low-FODMAP diet?

FODMAPs serve as food for the bacteria in the intestine. A diet low in FODMAPs may change the nutritional makeup of a person’s diet. People with a healthy intestinal flora should carefully consider whether they want to change the composition of the bacteria or microbiome through a low FODMAP diet. The exact influence of the low FODMAP diet on the microbiome is not well understood. In particular, the long-term consequences of the diet are not yet known, especially in people without IBS symptoms.

There is evidence that a low-FODMAP diet can inhibit the growth of positive bacteria and make the stool more alkaline, or increase the pH. For example, growth of bifidobacteria, ruminococcus gnavus, akkermansia muciniphila, and lactobacilli can be disturbed on a low-FODMAP diet. This can have negative consequences for intestinal health in a person without IBS.

For this reason, those living with irritable bowel syndrome should only carry out the diet together under the supervision of a nutritionist, and in partnership with their gastrointestinal specialist. Any co-occurring conditions can be carefully considered and closely monitored.

How is the FODMAP content of food determined?

The low FODMAP diet was first researched and popularized by Australian researchers. To measure the FODMAP content in food, researchers used high-performance liquid chromatography (HPLC) in conjunction with light scattering detectors called evaporative light scattering detectors, or ELSD. This technique allows the amount of fermentable carbohydrates (FODMAPs) in food to be measured.

Various books and websites provide recipes with low FODMAP foods for people on the diet.

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Shepherd, S.J., Lomer, M.C. and Gibson, P.R., 2013. Short-chain carbohydrates and functional gastrointestinal disorders. The American journal of gastroenterology, 108(5), pp.707-717. Online: http://www.nature.com/ajg/journal/v108/n5/full/ajg201396a.html, downloaded on 23.01.2016

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Dr. Sarah Toler, CNM, DNP

Dr. Sarah Toler, CNM, DNP

Sarah Toler is a Certified Nurse Midwife, Doctor of Nursing Practice, and science writer. She focuses on improving women's health and access to health care by working with digital health platforms. Her area of expertise is mental health, particularly the physical manifestations of stress and anxiety.

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