Fructose intolerance
Непоносимост към фруктоза

For most people, eating an apple or other fruit is the most natural and beneficial thing in their diet. For others, however, this causes a health problem. The reason is fructose, to which there may be intolerance.

For healthy people fructose intake is absolutely safe. It does not cause high blood sugar and is therefore most often used to make dietary products. People with fructose intolerance should follow a certain diet.

Fructose intolerance

What is fructose intolerance?

Fructose intolerance is an inherited genetic disorder, in which the person has little or virtually no enzymes involved in the breakdown and absorption of fructose.

Fructose is a monosaccharide used by the body to produce energy. It is also called fruit sugar because it is found in many fruits. Fructose is included in the chemical composition of some vegetables such as beans, cabbage, onions, tomatoes and others.

It is also found in honey, marmalades, jams, biscuits and other products, for which you may not even allow its presence. Note that many foods and beverages contain glucose-fructose syrup: juices, confectionery, ice cream, sweetened milks, sauces, etc. Its contents must be stated on the label and it is therefore advisable to read the information on the packaging carefully.

Fructose tastes sweeter than glucose, but unlike it, it dissolves in alcohol. Unlike glucose, the liver absorbs fructose twice as fast and does not require the intervention of insulin. This makes it suitable for diabetics, but in small amounts.

Studies show that each person can absorb different amounts of fructose. Even for healthy people there is a permissible amount, which is about 35-50 grams per day.

Fructose intolerance is due to a deficiency of the enzyme aldolase  C. Fructose malabsorption, as the disease is also called, manifests itself at an early age when eating foods containing fruit sugar.

Fructose intolerance

Fructose intolerance is transmitted in an autosomal recessive mode of inheritance, which means that it occurs if both parents suffer from this disease. Medical statistics show that boys and girls get sick equally often.

The disease was first described in 1956. The disease occurs with a frequency of 1:20 000 of the population. Congenital malabsorption of fructose is observed in Central European countries with a frequency of 1: 26 per 100 people.

Depending on the degree of enzyme deficiency, there are mild and severe forms of fructose intolerance:

  • In mild forms the symptoms are insignificant and the patient can sometimes eat small portions of products containing fructose;
  • Severe forms are manifested by an extreme degree of fructose intolerance, and its use causes acute hypoglycaemia (a condition in which the level of glucose (sugar) in the blood drops sharply).


 How is fructose intolerance detected?

The disease is usually detected in the first months of a child’s life or from the moment he or she begins to receive beverages and foods containing fructose. Symptoms of the disease appear immediately after adding sugar to food. Most often this happens during the feeding period, when fruit juices and mashed potatoes are introduced into the child’s diet.

It can occur earlier if the baby receives cow’s milk with added sugar as a food in mixed or artificial feeding. In case of early transition to artificial feeding with cow’s milk with sugar, children may refuse to eat. Vomiting is persistent and occurs after each meal, jaundice also appears.

Older children may show aversion to foods containing fructose and may not want to eat them. As a result, their body weight increases very slowly, hypotrophy gradually develops.

The child begins to lag behind in growth, his mental development slows down. Due to the fact that a lot of unprocessed fructose accumulates in the intestines, water from the blood and lymph begins to flow into it, which causes dehydration.

Adults may suffer from fructose intolerance even without knowing it and wonder why after eating fresh fruit or a sweet dessert their stomachs swell, they get a headache, their intestines begin to rebel and reach an upset stomach. Over time abdominal pain may become chronic, stomach pain may worsen, and the headache may turn into a migraine.

Gradually it can lead to worsening of sleep and depression. A person begins to get sick more easily because his immunity deteriorates. All these problems are actually due to the poor absorption of fructose in the small intestine. For this reason, it accumulates unprocessed in the large intestine, where putrefactive processes develop and many gases are released.

Fructose intolerance

During the anamnesis it is necessary to determine which foods cause the symptoms of the patient’s disease. Hereditary history is collected. The severity of the disease depends on the amount of food consumed.

Acute symptoms usually appear about 30 to 90 minutes after consuming foods or beverages containing fructose. They are:

  • Swelling of the abdomen
  • Flatulence (gas discharge)
  • Pain and gastrointestinal cramps
  • Nausea and vomiting
  • Diarrhea

Other symptoms are drowsiness, lethargy, intolerance to sweet foods, increased sweating. Intolerance to fructose can lead to weight loss. Shivering and convulsions may occur as a result of hypoglycaemia. However, children with fructose malabsorption have good oral and dental health.

The liver is enlarged in 70% of patients with fructose intolerance, especially in children in the first year of life. Jaundice develops. As the disease progresses, the liver becomes denser, its lower painful edge is easily palpated. Cirrhosis can develop with a prolonged course of the disease. Liver and kidney damage is more common in children under 1 year of age.

Patients with fructose malabsorption are more likely to develop depression. In people with fructose intolerance, folic acid levels are lower than usual, starting at age 35. Fructose malabsorption is thought to alter the intestinal flora, which is important for the body’s absorption of folic acid. The same effects can be found for zinc.

Patients who see a doctor for certain symptoms often have evidence of fructose intolerance in their medical history. Many patients have already tried the elimination diet and tell their doctor that their symptoms are improved by avoiding foods containing fructose.

Fructose intolerance

Not all people with fructose malabsorption show the characteristic symptoms. The diagnosis should be made by a specialist after a blood and urine test. Fructose stress tests are also performed. A reduction in blood sugar levels is observed in 75% of children with fructose intolerance and this occurs 20-60 minutes after fructose intake. It is accompanied by a feeling of hunger and sweating. Genetic tests are also performed.

If you have any stomach or other health problems and you suspect that they are related to fruit sugar, you can do a simple test yourself. First, eliminate all fructose-containing foods from your diet for a month. Then start consuming them again one by one, monitoring the reaction of your body. If your complaints return, the chances of not being able to absorb fructose well are high and it is a good idea to consult a specialist.

Fructose intolerance


What to do in case of fructose intolerance?

Unfortunately, there is no specific cure for fructose intolerance and treatment consists of following a diet. It is aimed at complete exclusion from the menu of foods containing fructose. This includes: fruits and all products containing such as jams, juices, compotes, canned food, pastries, honey and products  thereof (gingerbread, honey drinks), all products containing cane sugar and beets, which include glucose and fructose. Timely administration of a fructose-free diet can slow the progression of the disease. As soon as fructose stops entering the body, appetite is restored, vomiting stops, patients gain weight.

Diet therapy for newborns includes sugar-free dairy products. Infants receive dairy foods containing only lactose and dextrin-maltose. Instead of fruit purees and juices, food is supplemented with glucose.

When complementary foods are introduced earlier than in healthy children, meat, fish, cheese, eggs are prescribed. include in the child’s diet products from the prohibited list.

Older children and elderly patients are allowed to take milk and dairy products. However, powdered milk must be sugar-free (sucrose). Milk with added sucrose, condensed milk is forbidden. All types of cheese and natural fermented unsweetened dairy products are allowed. Meat, fish and eggs are allowed, but sausages and canned foods are excluded.

Fats are included in the diet almost without restrictions – butter, vegetable oils, margarine. Soy, flour with sucrose, biscuits, pastries, lemonade and all carbonated fruit drinks, juices, syrups, sugar, jam, pastries are prohibited.

Almost all fruits are prohibited. Lemons are an exception. Dried and candied fruits are also not allowed: apricots, plums, dates, etc.

Fructose intolerance

Of the vegetables are allowed green beans, lettuce, leeks, cabbage, spinach. Wheat or rye flour, rice, bread, semolina, tea, coffee and cocoa without sugar, glucose, maltose, dextrin-maltose, saccharin are allowed. All drugs containing sugar, sorbitol (granules, pills, powders, pills) are prohibited.

The prognosis is favorable in children who have been diagnosed in a timely manner and all fructose-containing products have been excluded from the diet.

Disease prevention comes down to genetic testing of parents who already have a child with fructose malabsorption or whose families have relatives with the disease.

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