Glucose Test: Checks for small intestinal bacterial overgrowth (SIBO), where bacteria in the small intestine can cause gas, bloating, pain, diarrhea, or constipation.

If positive: Treatment may include medication to reduce the overgrowth, addressing constipation or slow gut movement, and preventing recurrence.

Fructose Test: Checks whether fructose, a sugar in some fruits, honey, juice, and sweetened foods, is poorly absorbed and fermented by gut bacteria.

If positive: Briefly reduce high-fructose foods, then slowly add them back to find your personal tolerance.

Fructan Test: Checks sensitivity to fructans, carbohydrates found in wheat, onion, garlic, and some packaged foods.

If positive: Briefly reduce high-fructan foods, then slowly add them back to identify triggers.

A positive test is not a food allergy and does not mean you must avoid these foods permanently. The goal is the least restrictive diet that improves symptoms.

Dietitians are genuinely helpful. Studies show that patients working with dietitians achieve better compliance with dietary protocols, higher rates of symptom improvement, and are more likely to complete reintroduction and personalization phases successfully compared to those receiving only physician or self-guided education.

Sources:

Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American Consensus. The American Journal of Gastroenterology, 2017

ACG clinical guideline: small intestinal bacterial overgrowth. The American Journal of Gastroenterology, 2020

AGA clinical practice update on small intestinal bacterial overgrowth: expert review. Gastroenterology, 2020