Sugar malabsorption affects many individuals, causing symptoms like bloating, gas, diarrhea, and abdominal discomfort. When the body cannot properly absorb sugars such as lactose, fructose, or sucrose, they pass into the large intestine. Once in the large intestine, gut bacteria fermented the sugars producing hydrogen and/or methane gas. Measuring the levels of hydrogen and methane gas through breath tests provides important insights into how well the body is digesting these sugars.

How Sugar Malabsorption Breath Tests Work

During a sugar malabsorption breath test, the patient consumes a specific sugar (either lactose, fructose, or sucrose). If the sugar is not properly absorbed in the small intestine, it reaches the colon. In the colon, bacteria ferment it producing hydrogen (H₂) and methane (CH₄) gas. Then, hydrogen gas absorbs into the bloodstream which carries it to the lungs. When the patient exhales into the collection tube, the gas is collected and measured using gas chromatography.

By analyzing the rise in hydrogen gas levels during the breath test, clinicians determine whether malabsorption is occurring and to what extent. The greater the rise in hydrogen, the more significant the sugar malabsorption.

Diagnostic Criteria for Sugar Malabsorption

The following diagnostic thresholds are used to interpret malabsorption breath tests for lactose, fructose, and sucrose:

1. Hydrogen: A rise > 20 ppm above baseline during the breath test is diagnostic of malabsorption.
2. Combined Hydrogen and Methane: A rise > 15 ppm above baseline during the breath test is diagnostic of malabsorption 
3. Methane: A rise > 12 ppm above baseline during the breath test is diagnostic of malabsorption.

Common Trends for Each Sugar Malabsorption Test

Lactose Malabsorption (see Figure 1)

• Hydrogen Gas Trend: For individuals with lactose intolerance, a significant rise in hydrogen levels commonly occurs within 60 to 90 minutes after ingesting lactose.
• Diagnostic Interpretation:
  • A rise of 20 ppm or more indicates severe lactose malabsorption where the the small intestine absorbs little to no lactose.
  • An increase of 15 ppm or more indicates moderate malabsorption suggesting partial lactase deficiency.
  • A rise of 12 ppm or more indicates mild malabsorption. In this case, some lactose is absorbed, but not enough to prevent symptoms like gas and bloating.
• Symptoms: Common symptoms include bloating, diarrhea, and abdominal pain after consuming dairy products.

Fructose Sugar Malabsorption (see Figure 2)

• Hydrogen Gas Trend: In cases of fructose malabsorption, hydrogen levels typically rise 30 to 60 minutes after consuming fructose.
• Diagnostic Interpretation:
  • A rise of 20 ppm or more indicates severe fructose malabsorption, often causing significant digestive distress.
  • An increase of 15 ppm or more indicates moderate malabsorption, with symptoms occurring after consuming high amounts of fructose.
  • A rise of 12 ppm or more indicates mild malabsorption, where smaller quantities of fructose may still cause discomfort.
• Symptoms: Fructose malabsorption can lead to bloating, gas, diarrhea, and cramping after consuming fructose-rich foods like apples, honey, or high-fructose corn syrup.

Sucrose Malabsorption (see Figure 3)

• Hydrogen Gas Trend: For those with sucrose malabsorption, hydrogen levels typically  rise 30 to 60 minutes after ingesting sucrose.
• Diagnostic Interpretation:
  • A rise of 20 ppm or more suggests severe sucrose malabsorption, indicating a deficiency in the enzyme sucrase.
  • An increase of 15 ppm or more indicates moderate malabsorption, with symptoms occurring after consuming moderate amounts of sucrose.
  • A rise of 12 ppm or more indicates mild malabsorption, where some sucrose is absorbed, but not enough to prevent symptoms like bloating and gas.
• Symptoms: People with sucrose malabsorption often experience digestive discomfort after consuming sugary foods like candy, baked goods, and sweetened beverages.

What Do These Trends Mean?

The trends in hydrogen gas production during sugar malabsorption breath tests provide valuable insight into how well the body is absorbing specific sugars. A sharp increase in hydrogen levels, especially within the first 90 minutes, indicates a significant amount of undigested sugar is reaching the colon, where it is fermented by bacteria. The higher the hydrogen gas levels, the more severe the sugar malabsorption.

Understanding these hydrogen gas trends helps clinicians tailor dietary recommendations and treatment plans for individuals struggling with lactose, fructose, or sucrose malabsorption. For patients experiencing significant rises in hydrogen gas levels, reducing or eliminating the offending sugar from the diet can help manage symptoms and improve digestive health.

Prevent False Positives: Rule Out SIBO Before Sugar Malabsorption Breath Testing

SIBO can interfere with the accuracy of sugar malabsorption test results. Therefore, the North American Consensus for Breath Testing recommends ruling out Small Intestinal Bacterial Overgrowth (SIBO) with a glucose or lactulose breath test before testing for sugar malabsorption (such as lactose, fructose, or sucrose). If SIBO is present, bacteria in the small intestine may ferment sugars prematurely causing false positives during sugar malabsorption testing. By addressing SIBO first, clinicians can ensure that any malabsorption detected is due to enzyme deficiencies or transport issues rather than bacterial overgrowth.

This is part 2 of a three part series on common breath test trends. Read part 1 to learn about common trends for lactulose and glucose SIBO breath tests.