Symptoms
Possible symptoms of fructose malabsorption include:
- Abdominal pain, abdominal cramps
- Flatulence, bloating
- Diarrhea
- Constipation
- Gastroesophageal reflux (acid regurgitation), stomach burning.
- Nausea
Causes
The cause of discomfort is insufficient absorption of fructose (fruit sugar) from inside the intestine into the bloodstream. It enters the large intestine, where it is fermented by the bacteria of the intestinal flora, which triggers the symptoms. This fermentation produces gases such as hydrogen, carbon dioxide and methane, as well as short-chain fatty acids. This increases intestinal motility and leads to defecation. For osmotic reasons, water is also retained in the intestine when fructose concentrations are elevated, leading to diarrhea. Disorders in transport systems such as GLUT5, which are primarily involved in fructose absorption, are thought to be responsible for the reduced absorption. It is not an immunological disorder, i.e., not an IgE-mediated allergic reaction. It should also be clearly distinguished from the rare hereditary fructose intolerance, which can lead to organ damage. Fructose malabsorption can contribute to a relevant extent to the symptoms of irritable bowel syndrome and is considered common. Fructose occurs in the diet as a monosaccharide bound to glucose in sucrose (common sugar) and in oligo- and polymers such as the indigestible fructans. A small amount is usually tolerated. Typical foods containing fructose include fruit juices, apple juice, soft drinks, smoothies, fruit and bee honey. The usual intake capacity is 35 to 50 g. In fructose malabsorption, it is reduced to less than 25 g.
Diagnosis
Diagnosis is made on the basis of patient history, physical examination, and with an H2 breath test. This usually involves adults ingesting 25 g of fructose dissolved in 250 ml of water and then measuring the concentration of hydrogen in exhaled air over a period of time.
Nonpharmacologic treatment
- Complete avoidance of foods containing fructose is not required in fructose malabsorption and is not considered reasonable. Low-fructose dietary therapy is recommended. In this case, the amount of fructose is first reduced. Subsequently, it is tried individually, which foods are tolerated in what quantity.
- Glucose (dextrose) and galactose can improve the absorption of fructose, because the absorption takes place via the transporter GLUT2.
- Eat fructose-containing foods slowly because of the limited absorption capacity.
- Simultaneous consumption of protein- and fat-containing foods increases tolerance.
Drug treatment
Xylose isomerase is an active substance from the group of enzymes, which is used in the form of capsules as a medical device for the prevention and relief of symptoms of fructose malabsorption. The enzyme catalyzes the conversion of fructose into glucose in the small intestine, which is easily absorbed into the bloodstream. This prevents the fructose from entering the large intestine and causing discomfort. The capsules are taken before meals and are usually well tolerated. Symptomatic treatment: see under flatulence, diarrhea, constipation, abdominal pain, stomach burning.
