Fructose intolerance (synonyms: Fructose intolerance – hereditary (HFI); fructose malabsorption; fructose intolerance; fructosuria; fructosemia; fructose intolerance; fructose malabsorption; fructose intolerance; fructosuria; fructosemia; HFI; food intolerance; food intolerance; ICD-10-GM E74. 1: disorders of fructose metabolism) describes an intolerance to the carbohydrate fructose (monosaccharide/single sugar).
A distinction is made between the following forms:
- Hereditary fructose intolerance (HFI) – the metabolic disorder is congenital (rare).
- Intestinal fructose intolerance (IFI, fructose malabsorption) – the metabolic disorder is acquired (more common form) Fructose intolerance is caused by dysbiosis (disturbed intestinal flora) as a result of chronic stress such as long-term malnutrition, environmental pollution, toxins (eg xenobiotics), long-term stress or long-term use of drugs.
- Fructosemia – There is a failure of the enzyme fructokinase in the liver, which leads to an accumulation of fructose in the blood (frucosemia) and thus to an increased excretion of fructose in the urine (fructosuria). The so-called essential fructosuria does not require treatment and is diagnosed in most cases only by chance.
Intestinal fructose intolerance is a defect of the glucose transporter GLUT 5, which leads to incomplete intestinal fructose absorption. As a result, the transport system in the small intestine and thus the absorption (uptake) of fructose is disturbed in that fructose can no longer be transported through the small intestine into the blood and lymph channels. It does not migrate completely broken down into the colon (large intestine) and is broken down by the bacteria living there. As a result, about half of those affected suffer from symptoms of varying severity (mainly meteorism (flatulence), diarrhea). The symptoms are much milder compared to hereditary fructose intolerance and the reduced fructose absorption can be improved by the simultaneous intake of glucose.
Peak incidence: intestinal fructose intolerance occurs between the teenage and adult years.
The prevalence (disease incidence) of intestinal fructose intolerance is estimated to be 15-25% (in Western countries and Africa), of which about half present with symptoms. In Asia, the prevalence is about 10% of the total population.
The incidence (frequency of new cases) of hereditary fructose intolerance is about 1 case per 20,000 population per year and the incidence of essential fructosuria is about 1 case per 130,000 population (in Germany).
Course and prognosis: Hereditary fructose intolerance can be dangerous. If left untreated, it leads to liver and kidney damage as well as hypoglycemia (low blood sugar). Infants should not be given a diet containing fructose or sucrose (sucrose is a disaccharide/dual sugar consisting of one molecule of glucose and one molecule of fructose) too early. For the first four to six months after birth, infants should be fed exclusively breast milk or infant formula. If therapy is started early (fructose abstinence/renunciation), no permanent damage is expected. In intestinal fructose intolerance, affected individuals can usually tolerate small amounts of fructose. The tolerance threshold varies from individual to individual and must be determined by approach.