Do You Need a Breath Test for Fructose or Lactose Malabsorption?


Do You Need a Breath Test for Fructose or Lactose Malabsorption?


Breath Testing has been commonly used to diagnose intolerances to certain fermentable sugars (e.g. fructose and lactose) that are associated with symptoms of Irritable Bowel Syndrome (IBS) including gas, bloating pain, constipation or diarrhoea. But how accurate are they and can we use them to determine your diet?


Gut microbiome and gas production:

We all have about 1-2kg of bacteria residing in our intestines? We provide these bacteria with a food to eat and place to live, and in return they keep us and our guts healthy. When certain sugars (i.e. FODMAPs) are poorly digested in the small intestine they continue along the digestive tract to the large intestine. In the large intestine they are fermented by the resident bacteria and gases such as hydrogen and methane are produced as a side effect. In theory these gases can be measured in a breath test and the results used to potentially identify malabsorption of certain FODMAP groups.

In this article we’re going to cover what breath tests are, how accurate breath tests are, and what is the most reliable way to identify your IBS triggers.

So, what are breath tests? 

Breath testing is a non-invasive and low-cost way to measure sugar malabsorption. During this test you will be provided with a drink containing a dose of concentrated sugars such as lactose or fructose. Once you have had the drink, you will then be require to breathe out into a bag every 20 minutes over a 2-3 hour period to measure the level of Hydrogen in your breath.

A laboratory will then analyse the amount of hydrogen captured in the bag and report back to you if the amount was high or low. While a high hydrogen breath amount can identify that you malabsorb fructose or lactose, it doesn’t necessarily mean you are intolerant to them. Read on to find out why.

Should we interpret breath test results with caution? 

The short answer is YES. Although these tests are commonly used, the research shows they can be unreliable.

In 2016, Monash did a review of different studies to find out whether or not breath tests are reliable (you can read the study here). The research team found out that:

  • People suffering from IBS had the same results from breath tests as those without IBS. Meaning that these tests do NOT correlate with symptoms of IBS and don’t accurately detect if you can will suffer gut symptoms after consuming a given food.
  • Breath tests do not identify your threshold levels for a specific food i.e. how much can you eat before symptoms develop.
  • People can get different results if they do the breath tests on different days. In this study, 29% of IBS patients who tested positive to being fructose intolerant, tested negative 1 year later. Furthermore, they also found that between 20-25% of patients who tested negative to being lactose or fructose intolerant in a breath test actually, suffered with IBS symptoms when eating foods containing fructose or lactose.


Are the sugar drinks used in the breath tests the same as eating foods high in these sugars?

The short answer is No. Not only is there a huge variability in testing results and testing methods but the quantity of lactose or fructose given during breath tests can also be unrealistic when compared to your normal eating habits.

People doing breath tests are provided with up to 35g of fructose or 50g lactose to drink prior to the breath test. This is equivalent in fructose to 4 pears, 1 mango, and 3 teaspoons of honey in one sitting OR the amount of lactose in a full 1 litre of milk. Now, most people would not usually consume this much fructose or lactose in one meal. And, this much lactose or fructose can make everyone feel gassy or bloated, even if you do not have IBS.


Is malabsorption of FODMAPs dangerous?

Although malabsorption of FODMAPs can cause symptoms, it won’t shorten your lifespan and it doesn’t result in any damage to the body. In fact some FODMAPs (e.g. the Oligosaccharides) are supposed to be malabsorbed and are FODMAPs for all humans. In everyone they will ferment in the large intestine and create gas as a side effect. It’s just that some people have a more sensitive gut than others and this will be more aware of what is going on. This fermentation is actually a good thing because these foods and the gasses produced as a side effect have anti-inflammatory properties and contribute to keeping your gut microbiome healthy.

Managing malabsorption is purely about minimising any symptoms that result from eating a food and subsequently improving quality of life. Meaning that if a food doesn’t cause symptoms, it does not need to be limited. And, if it does cause symptoms, it only needs to be limited enough to minimise those symptoms and keep you comfortable. This approach will give maximum food variety and minimum symptoms, which ultimately is the ideal result.

Key points:

Breath testing alone does not determine:

  • If you have IBS
  • If you do not have IBS
  • If restricting certain foods will help your IBS
  • What your IBS is triggered by
  • How much of these foods you CAN eat before they trigger symptoms

If you have had a breath test and you were told that you malabsorb fructose or lactose then it’s important that you confirm the results with a food challenge. The same goes if you’ve been told you don’t malabsorb these sugars but are still having symptoms.


What you can do to get help with your symptoms?

A structured food elimination and challenge process can identify which foods trigger your symptoms (both FODMAP and non-FODMAP sensitivities) and what your threshold levels are for specific foods. People who follow this process guided by a specialised dietitian have been shown to get better symptom improvement and restrict less foods.

At Everyday Nutrition we are FODMAP trained qualified dietitians and nutritionists who specialise in managing all types of IBS and food sensitivities. We do virtual consults and you can receive personalized dietary advice on how to feel better by booking a consultation to get help from one of our friendly dietitians.

This article was written for Everyday Nutrition by Meher Vatvani and reviewed by Joanna Baker APD.

Meher is a Nutrition Science student who is passionate about gut health and nutrition. She loves cooking and baking.



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Meet Joanna


Joanna is a passionate advocate, communicator and educator in the fields of gut health, nutrition and wellness.