What are breath tests?
Breath tests are the most commonly used non-invasive tests for determining intolerances of various sugars (saccharides, e.g. fructose, lactose, fructans, sucrose) and sugar alcohols (e.g. sorbitol), also described as FODMAPs.
The breath test simulates what happens in real life in case of a sugar intolerance. The underlying cause of sugar intolerances is the reduced ability to digest and absorb sugars that have been eaten, leading to symptoms. The breath tests are well validated, although some discussion still exists regarding the ideal test conditions and test interpretation. The test procedure is identical for all the intolerances except for the sugar ingested. After standard preparation, including the exclusion of certain food and drink and smoking in the preceding 24 hours, the sugar of interest is swallowed. You then record the symptoms experienced and briefly breath into a special tube every hour for several hours. The breath test analysis and result are based on two factors:
- the symptoms experienced after swallowing the pure sugar. The symptom index is calculated based on the type and intensity of symptom reported and an increase in the index above a certain threshold is considered as evidence of intolerance.
- the concentrations of different gases measured in the exhaled breath samples. When sugars are not absorbed in the upper intestine, these malabsorbed sugars are fermented by the bacteria in the lower intestine mainly to short chain fatty acids (e.g butyric, acetic and propionic acids) and large quantities of gases. The types of gas produced depend on your bacterial flora. Most laboratories measure hydrogen in the breath samples, but it is important to also measure methane and CO2. An increase in the breath concentrations above a certain threshold after sugar ingestion is considered as evidence of malabsorption and as supportive of intolerance.
If an intolerance is diagnosed based on the symptoms and the breath gas concentrations a specific dietary treatment is possible and advisable. The success rates based on large studies, including our own, are at around 80% for adequate symptom relief.
The goal of the breath test is to identify the cause of the abdominal symptoms and then to advise an appropriate treatment.
Breath tests are safe and non-invasive and they can be performed in children (not under 6 years). Due to the nature of the test with the ingestion of a potentially poorly tolerated sugar, the typical intolerance symptoms may be caused during the test. This is, of course, part of the diagnostic importance of the test. In case of a positive test result a reduction in this class of sugar under the guidance of a professional dietician is advised. Symptom relief with appropriate dietary modification is expected within one week. Expert dietary advice is very helpful for the identification of food and drink containing the offending ingredient. Examples of ingredients difficult to identify on your own are so-called hidden lactose, or fructans and galactans in vegetables or whole-meal products.
How breath tests work
When sugars are ingested, they are normally digested (broken down) and absorbed in the small intestine (upper part of the intestine). If the sugars are not or not completely absorbed in the upper intestine, these malabsorbed sugars remain in the intestine and reach the lower intestine, where they are fermented by the bacteria (the flora) mainly to short chain fatty acids (e.g butyric, acetic and propionic acids) and large quantities of gases. This is the cause of the range of symptoms experienced. The types of gas produced depend on your bacterial flora. The gases produced are absorbed through the intestinal wall, pass into the blood and from there into the lungs and are then exhaled in the breath. An increase in the breath concentrations of hydrogen and/or methane (the most common gases produced besides CO2) above a certain threshold and the increase of symptoms after sugar ingestion are considered as evidence of an intolerance and malabsorption.
Why do breath tests?
To discover the commonest cause of food intolerances
Food intolerances are non-allergic reactions to food or food ingredients. In adults, food intolerances are much more common than food allergies, which is not the case in young children. The most common food intolerances by far are sugar-related (i.e. saccharides: e.g. fructose, lactose, fructans, galactans, etc, or sugar alcohols: e.g. sorbitol, xylitol, mannitol). These have been collectively described as FODMAP (fermentable oligo-, di-, monosaccharide and polyols) intolerances. The symptoms of sugar intolerances are varied, but overlap largely with those of functional gastrointestinal disorders, such as Irritable Bowel Syndrome or Functional Dyspepsia. Frequent symptoms are bloating, abdominal distension, gas, diarrhea or constipation, abdominal cramps, pressure or pain, nausea, increased intestinal sounds (borborygmi) and gastroesophageal reflux (GERD/GORD) amongst others. These symptoms may occur directly after eating the offending food, but may also appear many hours later.
Breath tests are the most commonly used and accurate non-invasive tests for determining or excluding sugar intolerances
The tests are safe, well-established and validated. Some discussion still exists regarding the ideal test conditions and test interpretation. These tests should not be used in infants and reduced doses of test sugars are used in children. The tests are easy to perform and are identical for all the intolerances except for the sugar ingested (See How to perform breath tests below)
The tests can now be performed at home, at the office or anywhere convenient
With the newest equipment it is possible to carry out the testing anywhere convenient. Most laboratories or clinics still require you to be onsite for several hours for testing for each sugar, but this is no longer necessary. The latest technology also no longer uses the large (re-used) breath bags, which then have to be returned quickly. With the new equipment (tubes) the samples are stable at room temperature for up to 2 weeks, so there is no pressure to return the samples immediately. In fact, they can be returned by post.
Identification of a food intolerance by breath testing will enable an appropriate and effective treatment resulting in reduction of your symptoms
If a sugar (saccharide or polyol, FODMAP) intolerance is diagnosed by breath testing specific dietary treatment is possible and advisable. The success rates based on large studies, including our own, are at around 80% for adequate symptom relief.
Which breath test shall I do?
Two possibilities: you think you have recognized an association between symptoms and certain foods, or, you don’t have a clue
Some individuals recognize a link between eating certain foods and the occurrence of symptoms. The symptoms of sugar intolerances are varied, but largely overlap with those of functional gastrointestinal disorders, such as Irritable Bowel Syndrome or Functional Dyspepsia. Frequent symptoms would be: bloating, abdominal distension, gas, diarrhea or constipation, abdominal cramps, pressure or pain, nausea, increased intestinal sounds (borborygmi) and gastro esophageal reflux (GERD/GORD) amongst others. These symptoms may occur directly after eating the offending food, but may also appear many hours later.
You think you have recognized an association between symptoms and certain foods
Examples of offending food groups easier to identify are dairy products (cause could be lactose intolerance or, less frequently, milk protein allergy), vegetables (cause could be fructans or galactans) or fruit (cause could be fructose or sorbitol intolerance, less frequently an allergy). Approximately 30% of individuals with one intolerance will also have a second intolerance (e.g. overlap between lactose and fructose intolerance, coincidence of fructose and sorbitol intolerances). A generally increased sensitivity to fermentable sugars forms the basis of the FODMAP theory. The racial background of the individual will make certain intolerances more likely. For example, lactose intolerance is more common in Asians or Mediterranean Europeans, fructose intolerance in Northern European and sucrose-isomaltose intolerance in native Greenlanders.
You don’t have a clue
If no offending food can be clearly identified it is reasonable to test for the commonest saccharide intolerances, lactose and fructose. It is important to exclude alarm symptoms for more serious disease (e.g. significant weight loss, blood in stools, long-lasting change in bowel habits, new abdominal pain, swallowing difficulty, especially in individuals over the age of 40 years). This exclusion should be performed by your doctor. If the lactose, fructose and fructan intolerance tests are negative, less frequent intolerances and reactions, such as sorbitol, sucrose or glucose intolerances, small intestinal bacterial overgrowth (SIBO), celiac’s disease and bile acid malabsorption should be considered.
The following breath tests (hydrogen, methane, CO2 measurements) are available
Fructose, lactose, sorbitol, fructans, mannitol, sucrose, glucose (useful for detection of small intestinal bacterial overgrowth). Lactulose (is no longer required as a routine test accompaniment to the above tests; can be used for estimating small intestinal transit time).
Choosing the test procedure
Which test procedure is best?
Increasing numbers of physicians, dieticians and laboratories are performing breath testing. There are differences in equipment and test procedures you should be aware of, as they influence the test accuracy as well as convenience.
Analyzers: Many test centers use handheld gas analyzers, which only measure hydrogen in your breath. This means 10-20% of intolerances will be missed, specifically those with a less usual intestinal flora (e.g. a methane-producing flora). The high-quality analyzers consequently measure methane as well as hydrogen.
Breath sample storage: There is a choice between handheld analyzers, where you blow directly into the machine onsite at the lab or clinic, and the more advanced analyzers which measure both methane and hydrogen where your breath is stored in a container until later measurement. With the latter, you will generally blow into a large, re-usable bag and the bag is connected to the analyzer for breath gas analysis within a few hours. This is more accurate than the handheld option, but still requires you to return the bulky bags to the lab within a short time span. The most recent improvement are the single-use vacuum tubes that can reliably store breath samples for at least 2 weeks. This system has several advantages. The testing can be performed at home or elsewhere without a rush and the tubes can then be returned by post. The tubes are single-use and therefore completely hygienic and safe. Additionally, CO2 is measured besides hydrogen and methane to automatically correct for any inaccuracies in the breath sample collection.
Duration of breath sampling: Most test centers perform regular breath sampling for up to 3 hours. It has recently been shown that up to 20% of intolerances are missed if sampling is discontinued after 3 hours, compared to sampling up to 5 hours. Hourly sampling is sufficient for intolerance testing.
Recording of symptoms: The diagnosis of an intolerance should be based both on the breath gas concentrations (demonstrating the malabsorption of the sugar) and the experience of symptoms (intolerance). Symptoms should be scored at the same time as each breath sample is collected. If there is only malabsorption (increased gas levels) and you experience no symptoms during the breath test, the link to the usual symptoms you experience is not proven. In fact, a certain percentage of healthy people will also have increased gas levels during the breath test, but no symptoms. The induction of symptoms during the test is an important confirmation that the malabsorption is related to your symptoms and that dietary advice for reducing the offending sugar is likely to be helpful in alleviating your symptoms.
Blood-sampling based tolerance tests, e.g. the lactose tolerance test, where blood glucose concentrations are measured after swallowing lactose, should no longer be used to test for intolerances due to a lower accuracy.
- Methane and hydrogen should be measured in the breath samples.
- The tube system is most advantageous, allowing testing at home or anywhere convenient.
- Measurement should be up to 5 hours after ingesting the test sugar.
- Conscientious preparation is required according to the instruction sheet
- Leave a gap of at least 4 days between tests, if multiple tests are performed.
How to perform breath testing?
Preparation for the breath test
Your symptoms are suggestive of a food intolerance, which can be tested using breath samples following swallowing of a specific sugar. Depending on the results 2 or 3 breath tests may have to be performed, each lasting approximately 5 hours on separate days. The breath test requires very specific preparations, as otherwise the results will not be valid. Please follow the below instructions carefully.
From 7 days before test
no antibiotics or colonoscopy.
From evening before test
no beans, peas, lentils, fruit, berries, honey, pasta, bread, dairy products (e.g. milk, yoghurt, soup or gravy mixes, cream, ice cream – butter and hard cheeses are fine) or chewing gum. An ideal meal would be rice with meat or fish, but without gravy, additives or vegetables. Please do not drink alcohol with this meal.
After midnight before test
no food or drink, except still water up to 2 hours before start of test.
From 2 hours before test
no smoking, no drinking, no chewing gum, no vigorous exercise. Brush your teeth, please!
- The test involves you blowing into a tube before and every hour for 5 hours after drinking the sugar solution. You must not eat or drink, except still water after 2 hours, until the test is completed.
- The test may well cause the same symptoms you normally feel, including bloating, stomach cramps/pressure, diarrhoea or nausea.
- Please fill in the form noting the type and intensity of symptoms you experience in the 24 hours following the test. Return the tubes within 2 weeks by prepaid courier, according to the included instructions. The information on the forms should be complete, as this is important for evaluating the test result.
Instructions for performing the breath test
The breath test is easy and safe to perform at home or anywhere else. You can see how the breath test is performed in the following two ways:
What if I do not have access to food intolerance breath tests?
Contact your local doctor to perform these tests or provide them for you.
If this is not possible: