fructose intolerance

Fructose intolerance: description

Fructose intolerance (fructose malabsorption) is a food intolerance in which fructose (fructose) is tolerated only partially or not at all. That is, fructose is not properly absorbed into the bloodstream in the small intestine. It enters the colon and is decomposed by bacteria. This produces gases that can often lead to abdominal pain or other symptoms.

Fructose is not only found in fruits and vegetables, but in many foods such as juices, beer, vegetables, honey and sweets. 15 to 25 percent of people in Germany suffer from fructose intolerance, according to the Deutsches Ärzteblatt (as of 2013). Researchers believe that this number will increase even further, as fructose is used as a sweetener in more and more finished products and beverages.

There is a congenital, as well as an acquired fructose malabsorption. The acquired form can disappear in the course of life or through a special diet.

Hereditary Fructose Intolerance (HFI)

One variant of fructose malabsorption is hereditary fructose intolerance. It occurs already in infancy. It is a congenital, potentially life-threatening defect of the fructose metabolism. Even small amounts of fructose can cause serious health complications for those affected. This form of fructose intolerance persists for a lifetime and also requires a lifetime of special diet.

The HFI is very rare. To illustrate the figure, the Journal for Nutritional Medicine works with the following size comparison: on the one hand of a population of 130,000, approximately 2,000 suffer from fructose intolerance, and on average one of them has hereditary fructose intolerance.

Fructose intolerance: symptoms

Everything important about the typical signs of fructose intolerance can be read in the article Fructose Intolerance – Symptoms.

Fructose intolerance: causes and risk factors

Even in people without fructose intolerance, the absorption capacity of fructose in the small intestine is limited. Normally 35 to 50 grams can be eaten without problems. If the diet exceeds this individual limit, the excess fructose enters the colon. There it is split by bacteria, it produces gases (including hydrogen, carbon dioxide and methane), but also short-chain fatty acids. These can cause discomfort such as flatulence, chair irregularities, diarrhea or constipation. If the food supplied contains few fats or proteins, the fructose is transported even faster through the small intestine. This restricts their recording.

Fructose intolerance is when less than 25 grams of fructose can be ingested. Affected so suffer from the consumption of small amounts of fructose to the corresponding consequences. In the case of hereditary fructose intolerance, however, no fructose is tolerated at all. This form of fructose intolerance can occur due to various gene changes and is inheritable. Already infants suffer from the typical symptoms.

Fructose malabsorption – impaired sugar transport

Normally, eaten sugars are split, and then added to the blood as single sugars in the small intestine. For this, various glucose transporters (GLUT) are available, which were numbered after their discovery. Fructose is preferably taken up via the glucose transporter number five (GLUT 5). A defect in this transporter limits the intake of fructose and leads to the clinical picture of fructose malabsorption. This defect can be both innate and acquired.

An acquired defect of GLUT 5 may be permanent or only temporary. This is influenced by several factors, such as how fructose is absorbed. Fructose is present not only as a single sugar in fruits, but also together with glucose (glucose) in ordinary table sugar (sucrose). This double sugar is first split into fruit and glucose and then absorbed by the sugar transporters in the intestine. Grape sugar stimulates the glucose transporter GLUT 5, so that fructose can also be better absorbed. For this reason, although it contains fructose, table sugar is usually well tolerated, even in the case of fructose intolerance.

Physical training on the other hand should worsen the transport capacity of GLUT 5. Just like the sugar substitute sorbitol (“sweetener”), which uses the same transporter as fructose and therefore rivals it.

Hereditary fructose intolerance – congenital enzyme deficiency

In hereditary fructose intolerance, there is an enzyme deficiency of aldolase B from birth. In fructose metabolism, fructose is gradually used to extract energy from multiple enzymes. One of these is aldolase B. If there is not enough, fructose is broken down much more slowly and other metabolites accumulate. In addition, sugar metabolism is generally inhibited. On the one hand, the sugar from the blood can no longer be burned to energy (glycolysis), and on the other hand, the body’s own sugar production is prevented at higher energy requirements (gluconeogenesis). This can lead to hypoglycaemia with corresponding symptoms. In addition, the resulting metabolites damage the liver, kidney and intestinal mucosa.

Fructose intolerance: examinations and diagnosis

The right person to contact if you suspect fructose intolerance is a specialist in internal medicine who specializes in diseases of the digestive tract (Gastroenterology). At the appointment, the doctor first inquires about your current symptoms and any previous illnesses (Anamnese). For example, he could ask the following questions:

• Do you often suffer from bloating, abdominal pain or bloating recently?
• Do you have irregular stool changes such as diarrhea or constipation?
• Have you discovered a connection with certain foods?
• Do the symptoms improve if you do without these foods?
• Is there a fructose intolerance for a family member?
• Do you suffer from a milk sugar intolerance (lactose intolerance)?

After the anamnesis follows the physical examination, The doctor listens with the stethoscope to the belly to check the bowel sounds. In addition, he taps and gropes his stomach, where he could notice increased air in the digestive tract.

Since the intestine can only be evaluated from the outside to a limited extent, further examinations are usually necessary for a diagnosis of fructose intolerance. Of the Fructose intolerance test, in which hydrogen is measured in the air, is thereby a central component of the diagnostics. In addition, a blood sample can be taken to detect a hereditary fructose intolerance and to exclude other diseases. Before a fructose intolerance test, a hereditary fructose intolerance must be excluded, as otherwise threatening hypoglycaemic conditions may arise.

Fructose intolerance test

If there is a suspicion of fructose intolerance, a fructose intolerance test is usually performed. To get a meaningful result, the patient must be fasting. At the start of the test, he blows into a device that measures the concentration of hydrogen in the exhaled air. Then he drinks a glass of water with 20 to 50 grams of dissolved fructose. Thereafter, further measurements are made every half hour. Overall, readings should be taken for at least two hours in a fructose intolerance test.

If fructose is restricted or not absorbed in the intestine, it is split in the colon by bacteria. This produces hydrogen (H2), which is transported to the lungs and then exhaled. An increased concentration indicates fructose malabsorption.

However, in some individuals with fructose intolerance, methane is produced in addition to hydrogen. In this case, hydrogen is consumed and can therefore no longer be detected in the breath. In order to detect a fructose intolerance in these individuals, the methane content of the exhaled air can also be measured.

Hereditary fructose intolerance test

If symptoms of fructose intolerance occur shortly after birth, or if close relatives suffer from hereditary fructose intolerance, a genetic test can be performed. In the process, typical gene changes are detected in the blood.

Fructose intolerance: treatment

The only treatment for fructose intolerance is a particular fructose intolerance diet. In hereditary forms must be completely dispensed with food with fructose. Not only solid food, but also drinks are part of the diet with fructose intolerance. Alcohol and sodas often contain fructose, which must be taken into account.

With an acquired fructose malabsorption, the diet is not quite as strict. In this case, it is even wrong to completely do without fructose. A fructose-free diet would initially improve the symptoms of fructose intolerance. Prolonged fruit sugar abstinence, however, reduces the number of sugar transporters in the intestine. Small amounts of fructose, which were initially well tolerated, can then cause symptoms. Initially, therefore, the fructose-containing foods should only be reduced. After a certain diet plan, the amount of fruit sugar can be continuously increased later. In some cases, even complete disappearance of fructose intolerance.

Fructose intolerance – Table

What do people eat on this diet? Which foods are problematic for fructose intolerance can be found in the article Fructose Intolerance Table.

Fructose intolerance: disease course and prognosis

A congenital fructification disorder such as hereditary fructose intolerance or the congenital form of fructose malabsorption persists throughout life. To avoid symptoms, a fructose-free diet must always be followed. While hereditary fructose intolerance can cause serious consequences such as liver and kidney damage even when in contact with small amounts of fructose, fructose malabsorption tends to lead to harmless digestive problems without long-term consequences.

In contrast, acquired fructose malabsorption can be positively influenced and even cured by a targeted diet. In some cases, it occurs only intermittently or disappears by itself. However, if it develops in adulthood, it usually lasts for life. As a rule, however, small amounts of fructose can be tolerated without having any symptoms fructose intolerance occur.