The low FODMAP diet – learn how to improve IBS symptoms

healthy stomach


Irritable Bowel Syndrome (IBS) is one of the most common digestive disorders and affects 1 in 7 adults. IBS has often been described as a “sensitive bowel” with people suffering from symptoms such as abdominal pain and bloating, and abnormal bowel habits such as diarrhea and constipation. Currently, there is no well-defined mechanism to explain why people develop IBS and there is still uncertainty regarding how best to treat IBS. Fortunately, there is a great deal of interest and research in IBS and plenty of theories are currently being tested.

Although there are no known cures for IBS, it is well known that lifestyle factors, stress levels, and diet all play an important role in IBS. People are often aware that certain foods will aggravate their symptoms, however it can be really hard to identify the specific trigger foods. Certain foods can lead to immediate bowel symptoms however this is not always the case. Food can take several days to pass through the digestive tract, and it may be a combination of foods consumed over the past few days that may be the cause of symptoms.

There has been a lot of interest and research involving the low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) diet. It is important to understand that foods are not thought to cause IBS, however, there are certain foods that will definitely worsen symptoms. One group of foods that have been shown to worsen IBS symptoms include the FODMAP foods. FODMAP refers to sugars found in certain foods that are poorly absorbed in the small intestine and pass undigested into the large intestine. In the large intestine (colon or large bowel) these small sugar molecules are fermented by the colonic bacteria leading to the production of gas which can lead to troublesome bloating and wind. These sugar molecules also attract water and can affect the motility of the colon leading to abnormal bowel habits including diarrhea and constipation.

FODMAPs are found in a wide range of foods including dairy, grains including wheat, fruit, and vegetables. The surprising thing is that many of the foods in the FODMAP group are relatively healthy foods. Many people try cutting out junk and processed foods however still have symptoms of IBS and are surprised that although eating a well-balanced diet, they still have significant bowel symptoms. It is important to remember that food serves a multitude of functions, and this can be very confusing when trying to work out the most suitable dietary plan. This is why it is very important to consult with a dietician regarding how to implement the low FODMAP dietary plan. Likewise, it is important to make sure that a medical physician has made a diagnosis of IBS before starting this dietary plan since serious medical conditions such as Celiac disease, Inflammatory Bowel Disease, and Colon Cancer can have symptoms which may be similar to IBS.


FODMAP refers to a large group of foods that contain dietary sugars that are poorly absorbed. The most common types of FODMAP foods include grains such as wheat products, onions, legumes, fruit, vegetables, and dairy. Fructose, or fruit sugar, and lactose, or milk sugar, are examples of dietary sugars that are found in FODMAP groups.  Most people have some level of difficulty in breaking down these sugar molecules. People with lactose intolerance have a relative deficiency in the enzyme lactase which is responsible for breaking down the milk sugar molecule lactose. When large amounts of dairy are consumed (such as more than a glass of milk),  people with lactose intolerance will suffer from diarrhea and bloating. This is exactly what is happening with other FODMAP sugar molecules in people with IBS. However, in people with IBS, it is not only dairy but also a whole range of other foods that can cause problems.

The FODMAP sugar molecules do not refer to only “sweet” sugars. The term sugar refers to a particular biochemical structure of carbohydrates, rather than to only the common table sugar that most people are familiar with. This small sugar particle can be fermented by gut bacteria leading to the production of wind, and can also draw water into the colon.

Although some FODMAP sugars can be partly absorbed, there are other FODMAP sugars that are not absorbed by anyone. For example, dairy products contain lactose which can be partly absorbed. People contain varying degrees of the enzyme lactase, and so excessive dairy consumption will only affect certain people. Other FODMAP sugars, on the other hand, will be undigested in everyone. Legumes and onions lead to gas production in most people. However, only people with a sensitive gut (IBS) will be affected by these foods.

For those who are technically minded, here is a table outlining the different types of FODMAP sugars:

List of FODMAP sugars

What effect do FODMAPs have in people with IBS?

FODMAPs are small particles which act to draw water into the digestive tract. Since these molecules are poorly absorbed in the small intestine they can be fermented by bacteria in the large intestine. This leads to the production of gas and increased flatulence. Most people are not bothered by increased gas production, however people with IBS will suffer from troublesome abdominal pain and bloating. The FODMAPs also lead to the increased fluid being drawn into the colon in an osmotic effect. The increased gas and fluid can alter the normal colonic motility leading to diarrhea and constipation. The main effect of reducing FODMAPs is to reduce bloating and wind.

Is everyone affected by FODMAPs?

Most people will experience a reduction in wind production when following a low FODMAP diet since there are some FODMAPs that are poorly absorbed by everyone. People with IBS, however, will be particularly affecting by FODMAPs. Since the colon is more “sensitive”, the increased wind and fluid that FODMAPs cause will lead to abdominal discomfort and bloating in people with IBS, whereas other people may develop any troublesome symptoms with FODMAPs.

Can I be tested for IBS?

IBS is a medical condition that is diagnosed on the basis of having certain clinical features. There is no current testing that can diagnose IBS, and so it is called a functional gut disorder. The results of all current testing, such as blood tests, stool tests, endoscopy, colonoscopy, and biopsy – are all negative. There are some conditions that share similar features with IBS, such as coeliac disease and inflammatory bowel disease. It is always important to consult with a medical physician to make sure that you don’t have a serious medical condition that might be mistaken for IBS. Sometimes further testing will be required to exclude serious conditions such as colon cancer.

IBS is currently considered to be a functional disorder and all current testing of the digestive tract is normal. Although all current testing is normal, this may well change in the near future. There is currently a large amount of research being undertaken in trying to work out the underlying mechanisms of IBS and it is likely that testing will evolve in the future.

Hydrogen breath testing is available which can help diagnose people who poorly absorb fructose, lactose, and sorbitol. Although breath testing can provide useful information, it is generally not required. Currently, the more common approach is following an elimination diet under the guidance of a dietician.

Should I follow the low FODMAP diet?

People with IBS should be considered for a trial of a low FODMAP diet under the supervision of a dietician. Hydrogen breath testing is available which can help diagnose people who poorly absorb fructose, lactose, and sorbitol. Breath testing, however, is generally not required and sometimes your doctor will recommend a trial of a low FODMAP diet. A Low FODMAP diet will help anyone who has symptoms of bloating and wind, however, it is important to note that dietary restriction should always be supervised by a dietician.

What are the foods high in FODMAPs?

This table shows foods that are high in FODMAPs. The most common types of food groups include grains such as wheat, onions, dairy, fruits, and vegetables. One of the most surprising things about this list of foods is that it contains many foods that are generally healthy. There are also many foods on the list and following this diet can be extremely daunting. Many people despair when they are given this information and give up even before starting this dietary plan. However, there are certain things that can be done that may increase your chance of success. Have a look at some of these handy tips below.

How to follow the low FODMAP diet successfully

There are some important principles to understand before starting this dietary plan.

1. The low FODMAP diet does not have to be a diet that you follow strictly lifelong. None of the foods on this list will cause any damage to your digestive tract – these foods may cause troublesome abdominal symptoms, but won’t actually cause any harm. This is quite a different situation to Celiac disease, where gluten products such as wheat actually cause damage to the small intestine. People with Celiac disease will need to follow a strict lifelong gluten-free diet. People with IBS can choose to follow a much more “relaxed” low FODMAP diet.

2. Think of the idea of a “threshold” when it comes to following the low FODMAP diet. For example, people with lactose intolerance often find that they can consume dairy products, however, if they have more than the equivalent of a glass of milk they may get abdominal symptoms of bloating and diarrhea. It is a similar concept with the low FODMAP diet – if you consume some FODMAPs you might be fine, however, there is probably a limit of FODMAPs that you can consume before you experience symptoms. Remember that people with IBS are often poor FODMAP absorbers and also have a sensitive digestive tract, and so FODMAPs may need to be limited.

3. The FODMAP diet will need to be individualized. The list of FODMAP provided are the most common foods which cause problems, however, you may find that you can eat certain foods on the list, whereas others will cause a major problem for you. The whole point of providing a low FODMAP diet is to give information that will help people to determine which foods they are sensitive to.

4. When bowel symptoms are particularly troublesome, a good approach is to follow a strict elimination diet for 6-8 weeks before slowly re-introducing food groups back into the diet. Another approach may be to target certain foods that you know to cause problems and only eliminate these from your diet. Wheat products tend to be a major problem for many people. Along with the agricultural revolution came an abundance of grains which are now the staple of the modern diet. Hardly a meal goes by in the day which doesn’t contain bread, pasta, or cereals. Nutritionists and naturopaths have long warned about the harm caused by grains, and diets such as the Paleo diet have made the concept of low grain diets popular. Although a certain amount of grains can probably be tolerated in our dietary intake, modern dietary intake of grains is probably excessive and should be limited.

5. Make a dietician your best friend. The best way to follow the low FODMAP diet is by planning ahead, and your chance of success is greatly enhanced by using a dietician. Ask your dietician for a low FODMAP shopping list, and make sure that you stock up your pantry and get a few good meal plan tips. Here are a few good pointers to get you started:

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