How to do a low FODMAPs diet

Healthy Diet

FODMAPs stand for: Fermentable Oligosacchrides, Disaccharides, Monosaccharides And Polyols

The low FODMAPs diet was developed by the Monash university as a way to help people with IBS symptoms. FODMAPs are short chain carbohydrates which are poorly absorbed in the intestines and fermented by gut bacteria producing methane and hydrogen gas.

FODMAPs are small and concentrated. The fermentation and osmosis caused by these undigested sugars can result in IBS symptoms such as gas, pain and diarrhoea. The short chain carbs have to be diluted by the body – so absorbing more water in the gut can create pressure, movement and diarrhoea.

The undigested sugars are fermented by bacteria in the large, and even the small intestines and produce gas. This can cause flatulence, bloating, abdominal pain and distention. In some people gas may slow movement through the bowel contributing to constipation.

What is a low FODMAPs diet, and how do I implement it?

The low FODMAP diet excludes high FODMAP foods from the diet whilst the cause of the complaint is identified and addressed. The diet should be followed for 4-6 weeks before the reintroduction. After 2-4 weeks, you should see a reduction in symptoms. If not, it’s likely another cause or the diet is not properly being adhered to.


  • Always check labels of food to make sure there aren’t any ingredients that you are supposed to be excluding.
  • Any fermentable foods should be made at home to guarantee the long fermentation process. E.g. store bought milk kefir/yogurt should be avoided.
  • Write down what you’re eating and your symptoms to help give you clues.
  • Doing a low FODMAPs diet can mean you may struggle to get enough fibre in the diet. Therefore it is important to include safe fibre foods like quinoa flakes, gluten free oats*, potato with skin, banana, raspberries, rice bran, vegetables, olives, swede etc.
  • Remember portion sizes as this too can play a role in total content of FODMAPs in the meal.

* not all coeliacs, can tolerate gluten free oats, replace for quinoa flakes, rice or buckwheat flakes instead.

FODMAPs diets are useful for:

  • Indicating presence of SIBO and reduction in feeding their bacteria IBS – particularly with distention, bloating, gas and diarrhoea Bacteria dysbiosis indicated from stool testing
  • Suspected lactose / fructose intolerance
  • The low FODMAPs diet should not be viewed as a resolution to the problem. The diet helps to manage symptoms while investigations and intervention is put in place to address the underlying triggers.

The FODMAPs diet is designed to remove fermentable fibres that may be aggravating the gut whilst testing is done and a protocol can be established to get rid of whatever is causing the problem. That can be yeast, bacterial, pathogens and food sensitivity etc.

Reintroduction phase:


  • Reintroduction is only performed once the symptoms have improved.
  • Test only one FODMAP group at a time.
  • Leave one week between introductions
  • Choose an amount of food that reflects a portion size – too little or too much may affect results.
  • Where possible choose a food that contains only one type of FODMAP.
    Continue to restrict all other FODMAPs until your tolerance or intolerance is confirmed.
  • Maintain a normal intake of alcohol and caffeine if you consume these – do not increase foods that you think may also be a problem for you.
  • Challenge with one FODMAP per week.
  • Eat the reintroduced food at least twice during the test week unless reaction in the first attempt in which case stop.

Intro 1: Polyols

Polyols should be introduced first as they are generally more tolerable than others.

Intro 1a: Sorbitol

Introduce one of the following: 1/4 ripe avocado
2 medium fresh apricots / 4 dried apricot halves

Intro 1b: Mannitol

Introduce one of the following: 1/2 cup mushrooms
1/2 cup of cauliflower

Intro 2: Lactose

1/2 – 1 cup of milk OR 6oz yogurt

Intro 3: Fructose

1/2 mango OR 1 tsp of honey

Intro 4: Fructans

Fructans and GOS should be tested last due to increased likelihood of intolerance. 1 garlic clove then build up to testing 1/4 onion (high fructan content).
(due to potential gluten intolerance- do not use gluten source as test)

Intro 5: GOS

1/2 cup lentil, kidney beans, baked beans or chickpeas.

If you DON’T get symptoms:

1. Increase the number of foods that contain FODMAPs you are testing and assess response

OR Maintain the amount and type of food you have tested and then undertake the next FODMAP food type.

If you DO get symptoms:

1. Wait until the symptoms are free again then reduce the serving size to half and try again

OR assume that the FODMAP is a problem for you and restrict these.

2. If unsure, try another food from within the same FODMAP group to confirm it is a problem.

3. The dose of FODMAP is vital – if you get symptoms then half the amount and try again but wait until symptom free. Consider challenge again in the future as sensitivity may change over time.

Why must I only do a low FODMAPs Diet for 4-6 weeks

A low FODMAPs diet takes out all the fermentable fibre. This is the energy source for beneficial bacteria in the gut which is crucial for healthy gut flora. It is necessary for the immune system, neurological communication, inflammation, allergic diseases, intestinal permeability, autoimmunity etc. FODMAPs deprive them of their food! Partculaly bifidifobacteria – one of the major groups that produce short chain fatty acids. When you restrict carbohydrate, bifidido goes down. Butyrate is one of these which is needed for reduction of inflammation in IBS. The total diversity of gut flora goes down.

For these reasons, a low FODMAPs diet is only safe during a short period of time and must not be followed long term. During this time you can supplement with bifidobacteria and butyrate.

FODMAP food groups:


Fructose is absorbed in the small intestines with the help of glut-4 transporters which need glucose to help. People absorb fructose slowly (as is the norm), but it may be even slower in some. Around 30-40% will not absorb fructose. Glucose is important in the absorption of fructose. The ratio of the two in foods influences whether the food is considered a High or Low FODMAP food.

When fructose occurs with glucose it is well absorbed because the glucose aids it across the bowel.

In order to work out if a food is high FODMAP or not, you need to know how much glucose it contains. Look at the ratio of fructose and glucose. If fructose is in higher concentrations then the absorption is slower. Foods are often considered a problem if they contain more than 0.2g of fructose in excess of glucose per serving.

e.g. Honey contains 40g fructose per 100g, and 30 grams of glucose per 100g – this means and excess of 10 grams per serving = too high.

Kiwi contains 4 grams fructose per 100g and 4g glucose = no excess = good to go!


Disaccharide sugar (glucose and galactose) present in some dairy products. A lactose free diet is NOT the same as a dairy free diet. Absorption requires lactase to breakdown lactose. Lactase is often low in newly diagnosed coeliacs where villi are damaged.

The older you get, the more likely you are to have a problem as it’s about the amount of lactase you produce to digest. IBS and coeliacs can influence the amount of lactase they can produce. Once the inflammation and damage is repaired, this may get better.

Lactase splits the lactose into two monosaccharides (single sugars: glucose and galactose). If you struggle with producing lactase and cannot break down large quantities of lactose, it moves into the colon intact where they are fermented by the resident microorganisms – resulting in the common symptoms of gas production causing abdominal bloating, pressure, pain, wind and diarrhoea.

Symptoms can arise 30 mins to 2 hours after consumption but hard cheeses don’t contain as much lactose as milk and softer cheeses. You therefore be able to tolerate a small spread of butter on toast or a slice of cheddar cheese.


Polyol sugars include, Sorbitol, Mannitol, Xylitol and Erythritol. These are only absorbed passively across the small intestine.

Sorbitol and mannitol are most common in the diet. Sorbitol is found to be more of a problem for those with digestive symptoms. Because sorbitol can be such a problem, it may be best to introduce them separately. Moderate sorbitol in the following should be limited. e.g. avocado = 1/8


Fructo-oligosaccharides (FOS) and inulin. We lack the enzymes to break down fructans and GOS. Therefore most people with IBS will have problems with these foods. They are considered a problem if they contain more than 0.2g of fructans per serving of cereals and 0.3g of fructans per serving of other food.


Galacto-oligosaccharides (GOS) are short chain molecules formed from galactose sugars joined together with a fructose and glucose at the end. Raffinose and stachyose are the most common GOS in foods – they are particularly evident in beans, legumes, lentils etc

High GOS foods are those that contain more than 0.2g per serving. Some people may be able to cope with a small amount of canned and rinsed chickpeas for example.

For more information regarding what foods are considered high or low FODMAP, take a look at the Monash University FODMAPs page or download their app.


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