In searching for why a child might have chronic bellyaches or other gastrointestinal symptoms, I often come across doctors ordering a test called a “fructose breath hydrogen analysis.” Every now and then, a parent seeks my advice about their child’s test results. Although I’ve never ordered the test myself, I decided to write this blog post to help answer the most common questions I get from parents.
What does a fructose breath analysis test for?
This test is done to determine whether someone is able to digest fructose normally. If the test is positive, then the child has fructose malabsorption.
What is fructose?
Fructose is a sugar (carbohydrate) molecule. When found in nature, fructose is what makes fruits, vegetables, honey, agave syrup, nectar, etc., sweet. Fructose also is also added to many packaged and processed foods as a flavoring agent and preservative. Fructose also is present in sucrose, the scientific term for the white powder we commonly refer to as sugar.
Sucrose is considered a “disaccharide” because it’s formed when two separate molecules (glucose and fructose) are linked together. On their own, fructose and glucose are each “monosaccharides.” Starches, on the other hand, are polysaccharides, formed when multiple monosaccharides are linked together to form complex chains.
How is fructose normally absorbed?
Depending on the number of molecules found within a specific carbohydrate, our gut is designed to be able to digest it using a combination of enzymes and transporters. For instance, lactose (a disaccharide) is first digested by the enzyme lactase into one molecule of glucose and one molecule of galactose. Then each of these single molecules attaches to specific receptors found on the cells lining the small intestine. These receptors “suck” in the individual sugar molecules so that they can be absorbed.
Fructose digestion and absorption differ from that of the other carbohydrate molecules. First of all, no intestinal enzyme exists to break it down. Lactose requires lactase and starches require amylase, but fructose doesn’t require an enzyme. Fructose is absorbed passively through the lining of the intestine.
Fructose’s other unique characteristic is that it’s a sugar molecule which, under normal circumstances, we don’t even require for human survival. While glucose is the “sugar of life” and is important for every cell in the human body to survive, fructose can only be used and stored by the liver. In fact, ingestion and absorption of excessive amounts of fructose can actually lead to disease. This includes liver and heart disease and problems such as insulin resistance.
What is fructose malabsorption?
When the amount of fructose ingested exceeds the amount that can be absorbed through the gut, the remainder gets passed further along into the lower intestinal tract. Along the way, the unabsorbed sugar “feeds” the trillions of bacteria normally present, especially in the colon. The bacteria ferment fructose into energy for their own nourishment, releasing hydrogen gas in the process.
When the unabsorbed fructose gets all the way to the last part of the colon, it mixes easily with water, just as any sugar or salt, and causes watery stools.
It’s these physiologic processes that lead to the typical symptoms of fructose malabsorption -- gassiness, bloating, explosive and/or watery diarrhea, nausea and abdominal pain.
Is fructose malabsorption the same as fructose intolerance?
Parents need to be mindful not to confuse fructose malabsorption with fructose intolerance, also known as “hereditary fructose intolerance,” or HFI. HFI occurs when a child is born without one of the key enzymes that the liver needs to metabolize fructose. The absence of this enzyme causes toxic accumulation of byproducts that can lead to potentially life-threatening liver, kidney and neurologic problems.
Is fructose breath testing useful?
During the fructose breath hydrogen test, or FBHT, a child is given a weight-based dose of fructose after an overnight fast. The test is considered positive if there is a significant increase of hydrogen in the child’s breath sample, which is collected at 30-minute intervals for up to three hours. Below is an example of an actual test report, brought to me last month by the concerned parent of a 3-year-old. The test is positive, showing that the child does malabsorb fructose.
As I mentioned earlier, to be absorbed, fructose must first attach to a receptor found on the lining of the intestinal wall. The number of receptors increases with age, so infants and toddlers have more fructose malabsorption than older children and adults. And since excessive fructose absorption can lead to disease, humans are designed to be able to malabsorb some.
The problem with the fructose breath hydrogen test is that if given enough fructose, almost any child will test positive. This is particularly true for younger children, provided they have a relatively typical population of gut bacteria, most of which will ferment fructose into hydrogen!
In 2011, the American Board of Internal Medicine launched Choosing Wisely, an effort to engage patients and physicians to become better stewards of health care resources. Partnering with Consumer Reports, there are now published lists available to the public, informing us of inappropriate and overused tests.
Personally, I believe the fructose breath hydrogen test should be added to the list. It is performed frequently but I believe it offers no benefit. Moreover, it’s relatively costly and could lead to harm.
How can fructose breath testing lead to harm?
In my own practice, I have seen children who had positive fructose breath hydrogen tests end up in two harmful scenarios.
The parents of a child with a serious inflammatory condition of the intestinal tract are led astray by the results of a fructose breath hydrogen test. The positive results lead to the elimination of all sugar in the child’s diet. This temporarily improves the child’s well-being, but eventually the symptoms return. I recall a 13-year-old boy I met six years ago whose diagnosis of Crohn’s disease was delayed a year because it was assumed he suffered from fructose malabsorption.
Little did he, his family or his health care providers realize that the severity of his symptoms with fructose were merely secondary to the underlying intestinal inflammation caused by Crohn’s disease! Eventually, the worsening of his diarrhea and other symptoms, despite strict dietary elimination, led him to seek a gastroenterology consult, which led to the correct diagnosis. Once the Crohn’s disease was treated, he was able to start eating fruit again, without experiencing severe diarrhea or any other bothersome symptoms.
In the second scenario, the parents of a child who has no serious medical conditions are told their son or daughter has a positive fructose breath hydrogen test and needs to stop eating all fructose. This leads the family to incorrectly believe that even small amounts of fructose are dangerous and harmful to the child, and all sources of fructose (including fruits and vegetables!) must be eliminated from the child’s diet forever.
- Since excessive fructose absorption can lead to disease, humans are designed to be able to malabsorb some.
- To avoid troublesome symptoms associated with fructose malabsorption, reduce the amount ingested. Remember that the amount of fructose in dried fruit, syrups, honey and juice is much greater than the amount found in fresh fruit, and that the fiber in whole fruit helps prevent harm.
- Fructose is not necessary for human survival, but eating seasonal fruits and vegetables is not harmful and generally recommended.
- Do not confuse fructose malabsorption with hereditary fructose intolerance.