SIBO Breath Test: Glucose or Lactulose?
You might have heard of the SIBO Breath Test. But there are a few options…it can be hard to determine which is best for you.
In this article, I explain what is the SIBO Breath Test, how it works, and I go through the most common options for patients that wish to test for SIBO.
What is the SIBO Breath Test?
Small Intestinal Bacterial Overgrowth (SIBO) breath testing is a simple yet important diagnostic tool for identifying bacterial overgrowth in the small intestine. The two primary substrates (controlled sugar substances) used in these tests are Glucose and Lactulose (not to be confused with Lactose). Each substrate has its advantages and downsides, and understanding these can empower you into seeking answers and clarity on your digestive health.
Who Should Get Tested for SIBO?
There are many symptoms that can be linked to SIBO, such as bloating, abdominal pain, belching, flatulence, nausea, fatigue, brain fog, and irregular bowel movements (constipation and/or diarrhea). However, due to the nonspecific nature of these symptoms, confirming SIBO requires a test. SIBO is now considered a primary cause of IBS.
For this reason, anyone diagnosed with IBS or experiencing the symptoms mentioned above may want to consider testing for SIBO. There are also a few key conditions that have been highly correlated with SIBO, such as Fibromyalgia, Rosacea, Chronic Fatigue Syndrome, Ulcerative Colitis, and Hypothyroidism. Individuals dealing with any of these conditions could benefit from taking a SIBO Breath Test.
How Does the SIBO Breath Test Work?
The SIBO breath test works based on the fact that bacteria ferment carbohydrates, resulting in the release of gas, including hydrogen, hydrogen sulfide and methane. While approximately 80% of this gas is expelled through the intestines, the remaining 20% is absorbed into the bloodstream and circulates to the lungs, where it is exhaled. By measuring the gas levels in your breath, a laboratory can estimate the extent of bacterial overgrowth as the substrate makes its way into your digestive tract. Taking into consideration one’s transit time is important.
This aspect is crucial to understand—the laboratory doesn't directly measure the bacteria; instead, it utilises the gas as an indicator of the type and quantity of bacteria present. While certain SIBO breath tests exclusively measure hydrogen, a more comprehensive approach involves measuring both hydrogen and methane for a more precise assessment of potential overgrowth, which is what I recommend in my practice. There is also a newer test available in the United States called trio-smart, which also measures Hydrogen Sulfide gas levels.
At-home SIBO Tests from reputable laboratories are as reliable as the ones done at the doctor’s office. Make sure to follow the instructions closely, especially the prep diet.
Be wary of hand-held devices like the ones from FoodMarble that claim they can be used for SIBO testing. While highly promising, I have seen many inaccurate results from these devices. It is preferable to complete an at-home test from a proper lab (typically using Quintron technology) for clear, actionable results.
Which is Better: Lactulose or Glucose?
A quick reminder that the small intestine is actually long in length: it ranges from about 10 to 22 feet, or 3 to 7 meter. This means that there is a vast (long) environment to cover when doing SIBO testing.
SIBO Lactulose Breath Test
Advantages:
Greater Sensitivity: Lactulose is an indigestible sugar, meaning it travels throughout the small intestine unchanged, enhancing its sensitivity to possible bacterial overgrowths in both proximal (earlier part) and distal regions (latter part of the small intestine).
Comprehensive Testing: The lactulose breath test typically lasts three hours, allowing for a more comprehensive assessment all the way into the colon. This could also be seen as a downside, however, as individuals with a faster transit time could be falsely diagnosed with SIBO if it reaches the colon sooner than the cut-off timing of 90 minutes, where the transition between the small intestine and large intestine is presumed to happen. I personally tend to use the European cutoff timing standard of 60min in order to avoid these false positives.
Sometimes we see a rise only after the 90-min mark, and in that case it is indicative of potential dysbiosis in the colon or LIBO.
Downsides:
Less Specificity: Lactulose can be fermented by both bacteria and yeast, potentially leading to false-positive results for bacterial overgrowth. It would however indicate a case of SIFO, which needs to be addressed as well.
Extended Test Duration: The longer testing duration may be inconvenient for some individuals. It is also not always necessary to test past the second hour after the ingestion of the substrate, as we can be fairly certain that it has reached the large intestine by this point, especially since Lactulose is known to quicken the transit time (after all it is a laxative).
SIBO Glucose Breath Test
Advantages:
Specificity: Glucose is absorbed higher up in the small intestine, making it more specific for detecting SIBO in the proximal (early) small bowel, if this is what we suspect.
Shorter Test Duration: The glucose breath test typically lasts two hours, making it a quicker option for those with time constraints.
Downsides:
Less Sensitivity / False Negatives: Glucose gets absorbed fairly quickly in the small intestine, so it may not reach the distal (latter part of the) small intestine. This could lead to missing the presence of overgrowths in this region.
Blood sugar spike and crash: The glucose breath test requires the individual to ingest about 75g of glucose on an empty stomach after a fasting period. This can cause an important sugar spike and could potentially further aggravate those with blood sugar dysregulation.
The Duration of the Test: Is it Important?
The duration of a SIBO breath test is a factor for the practitioner to consider in obtaining accurate and comprehensive results. The test's duration determines the timeframe over which the ingested sugar (substrate) travels through the digestive system, influencing the identification of bacterial overgrowth.
As we know, we do have a large number of bacteria in the large intestine (colon), which is absolutely normal and we wouldn’t want to interpret it as a small intestine overgrowth when the sugar has in fact reached the colon.
If we suspect a slower transit time, a longer test could be indicated. There is unfortunately no way to know your orocecal transit time unless you do the breath test procedure alongside a scintigraphy in a medical center setting (a very rare occurence).
In summary, the choice between test durations depends on the suspected location of bacterial overgrowth and the desired specificity and sensitivity of the test.
Choosing between glucose and lactulose for a SIBO breath test involves weighing the advantages and downsides of each substrate. While glucose may be more specific for proximal overgrowths, lactulose offers greater sensitivity across the entire small intestine.
I still continue to use the Lactulose Breath Test for most of my patients as I find it more accurate for the vast majority of people. This is usually where I start, and if needed, will recommend testing with a second substrate.
Consulting with a SIBO practitioner is crucial not only for selecting the most appropriate testing method but also for accurate interpretation of the results.