Chronic abdominal pain, fatigue, and unexplained low blood sugar levels may be signs of a rare condition known as fructose intolerance, experts from the School of Public Health at the University of Queensland (Australia) told The Conversation.

According to the researchers, people with fructose intolerance lack a key enzyme — aldolase B — which is essential for breaking down this type of sugar. The disorder is rare, affecting approximately one in 10,000 people. Hereditary fructose intolerance is passed on genetically when both parents carry the same mutation.

The scientists emphasized that fructose intolerance is very different from food allergies. In allergies, the immune system reacts to components of food as if they were harmful pathogens, leading to hives, swelling of the mouth, or difficulty breathing. In fructose intolerance, by contrast, the symptoms are not related to the immune system.

“In infants and young children, fructose intolerance may present as unusual sleepiness or irritability, refusal to eat, or vomiting. In adults, symptoms may include chronic abdominal pain, fatigue, and unexplained hypoglycemia. Doctors may also notice subtle signs such as an enlarged liver, abnormal liver test results, or signs of fatty liver disease,” the researchers explained.

Experts reminded that fructose is not only found in fruit — it is also present in honey, certain vegetables, sweetened beverages, cakes, cookies, sauces, and bread. Fructose is also added during the processing of some meats (such as sausages) and dairy products.

“Sucrose (table sugar) and sorbitol (a sugar substitute commonly used in chewing gum, toothpaste, and medications) also contain fructose or are converted into it during digestion. This means that people with hereditary fructose intolerance cannot safely metabolize these sugars either,” the experts warned.