Intestinal fructose intolerance is an intolerance to fructose (intestinal means that the disease affects the digestive tract, fructose is fruit sugar, intolerance means intolerance). It manifests itself mainly in digestive symptoms.
What is fructose intolerance?
Fructose intolerance is a digestive disorder in which fructose from food cannot be adequately absorbed in the intestine (malabsorption), causing discomfort in the large intestine. In Germany, about one in ten people is affected by fructose intolerance; the incidence of frutose malabsorption is put at about one third of the population. There is also a heriditary form of fructose intolerance, which is due to a genetic enzyme defect; however, this is extremely rare and clearly distinguishable from the far more common intestinal fructose intolerance.
Causes
Intestinal fructose intolerance is initially caused by fructose malabsorption. Due to a malfunction of certain transport proteins, fructose cannot be completely absorbed in the small intestine and thus reaches the large intestine in excessive amounts. This malabsorption is not unusual in itself and probably has no clinical significance. In the second step, an intestinal disorder specific to fructose intolerance causes the fructose present in the large intestine to lead to digestive problems. Diarrhea, flatulence and abdominal pain occur. The exact mechanism leading from fructose malabsorption to fructose intolerance has not been conclusively clarified. The influence of stressors such as taking antibiotics or hormonal fluctuations on the development of fructose intolerance is discussed, but has not been adequately proven.
Symptoms, complaints, and signs
In fructose intolerance, symptoms occur that can also occur in other diseases. Therefore, it often takes a long time before the correct diagnosis is made. The typical symptoms appear immediately after eating a meal containing fructose. There is strong gas formation in the intestine, flatulence, diarrhea, abdominal pain, nausea, vomiting and colicky cramps. Furthermore, fatigue, headaches, dizziness, increased susceptibility to infections, weather sensitivity and depression often occur. The gas formation and flatulence are due to the decomposition processes of fructose not absorbed by the intestine. In the less common hereditary fructose intolerance, fructose is absorbed by the intestine but cannot be sufficiently broken down. The resulting increase in fructose concentration in the blood displaces glucose. This can lead to dangerous hypoglycemia, impaired consciousness and liver dysfunction. The affected infants therefore suffer from failure to thrive without a strict low-fructose diet. However, about 30 percent of all patients are completely symptom-free. The reasons for the different manifestations are not yet fully understood. However, some possible secondary complaints of a fructose intolerance are known. These include damage to the intestinal mucosa, disturbance of the intestinal flora, weakening of the immune system, and folic acid and zinc deficiency. The damage to the intestinal mucosa can lead to other intolerances such as lactose intolerance and histamine intolerance. The disturbance of the intestinal flora makes itself felt through frequent diarrhea or even constipation as well as other digestive disorders. Folic acid deficiency is often the cause of depression, irritability and concentration problems.
Diagnosis and course
Fructose intolerance initially manifests as digestive symptoms such as diarrhea or constipation, pain and cramps in the intestinal area, and flatulence and bloating. Untreated fructose intolerance can also result in irritable bowel syndrome and heartburn. Due to the disturbed absorption of nutrients from the intestine, severe fatigue and exhaustion, even depression and a general weakening of the immune system can occur. Frequently, there is a deficiency of zinc, folic acid and tryptophan. Fructose intolerance can be diagnosed by a simple hydrogen breath test. This measures the concentration of hydrogen in the breath before and after the ingestion of fructose. An elevated concentration demonstrates the presence of fructose intolerance. Alternatively, measurement of the fructose plasma level in the blood is also possible.
Complications
In the common form of fructose intolerance, complications rarely occur. These are mainly to be expected if fructose is ingested in larger quantities despite the already recognized intolerance. The situation is different with congenital – the so-called hereditary – fructose intolerance. This already affects infants. This congenital defect in fructose metabolism is potentially dangerous and life-threatening. The enzyme-related intolerance of fructose can lead to a whole series of health complications. These are caused by the ingestion of even the smallest amounts of fructose. As a countermeasure, a strict low-fructose diet must be followed throughout life. The reason: the congenital enzyme deficiency slows down the breakdown of fructose. A frequent complication of congenital fructose intolerance is disturbances in sugar metabolism. In particular, the risk of hypoglycemia is high in hereditary fructose intolerance. In the worst case, hypoglycemia can lead to impaired consciousness and coma. Often there is hyperacidity in the body, so that a metabolic derailment is present. At the same time, the slowed breakdown of fructose leads to metabolic products that damage the liver, kidneys and intestinal mucosa. This results in kidney dysfunction, including acute kidney failure, or liver dysfunction. Liver cirrhosis can also develop. In addition, hereditary fructose intolerance can lead to coagulation disorders.
When should you see a doctor?
If a digestive disorder occurs repeatedly a short time after food intake, a doctor should be consulted. In case of flatulence, pain in the abdomen or stomach, a feeling of pressure inside the body or heartburn, a visit to the doctor is necessary. A persistent feeling of malaise, nausea, vomiting or an elevated body temperature must be examined and treated by a doctor. If the affected person suffers from a diffuse feeling of illness, general weakness or disturbances in concentration, he or she needs medical help. Reduced performance, fatigue and persistent tiredness should be discussed with a physician. If diarrhea, constipation or irregularities in urination occur, the symptoms should be presented to a physician. If the symptoms persist for several days or weeks, this is considered unusual and they should be clarified by a doctor. If changes in the appearance of the skin occur, itching develops or open wounds appear, a doctor must be consulted. Pathogens can enter the organism via the wounds and cause further illnesses. If attention deficits or inner restlessness occur, a doctor should be consulted. If emotional or mental problems arise, it is necessary to consult a doctor or therapist and ask for help. In case of depressive moods, a withdrawal behavior or aggressive behavioral traits, a visit to the doctor is necessary.
Treatment and therapy
Because the exact mechanisms of fructose intolerance are as yet unknown, no causative or curative therapy exists. The only form of treatment is to avoid foods containing fructose. This is not without problems, since fructose is increasingly found in foods that are considered beneficial for a healthy diet (fruit, some vegetables, but also numerous diabetic and light products). Fructose is also increasingly used in industrially produced and highly processed foods, especially as a sweetener. Even ordinary household sugar consists of half fructose. For this reason, professional nutritional advice is recommended. If the intake of fructose is reliably reduced, the symptoms usually improve noticeably and patients can usually live symptom-free if they adhere to the appropriate diet. How strictly this diet must be adhered to, or what amounts of fructose can still be tolerated without symptoms, varies greatly from person to person. In addition, a dietary supplement called Fructosein is available that converts fructose into glucose in the intestine when fructose-containing foods are ingested, thus preventing the intolerance reaction. Fructose intolerance often occurs in conjunction with lactose intolerance, which also results in similar symptoms. Additional testing of lactose tolerance is therefore recommended for all patients with fructose intolerance.
Outlook and prognosis
The prognosis is different for the three known forms of fructose intolerance. Acquired intestinal fructose intolerance or fructose malabsorption is a treatable metabolic problem. This is based on an intestinal dysbiosis. Intestinal dysbiosis can be successfully treated with appropriate measures. The prognosis is positive. However, it can take longer for the intestinal flora to regain its balance. The chronic intestinal stresses must be eliminated and the intestinal flora must be rebuilt. Then it can be tested which fructose amounts are tolerated. Usually small amounts of fructose are tolerated. In the case of fructosemia, the prognosis is also positive. Failure of an enzyme called fructokinase, which is present in the liver, is rarely noticeable. Fructose accumulates in the blood. It is excreted in the urine. In this respect, there is no damage to health. In the congenital and rarely occurring hereditary fructose intolerance (HFI), there is a deficiency of the enzyme fructose-1-phosphate aldolase B. The fructose is not present in the liver. As a result, this form of fructose intolerance can manifest with severe effects. If this disorder is not treated promptly, liver and kidney damage are the result. Dangerous hypoglycemia may occur. To protect infants from the effects of hereditary fructose intolerance, they should receive only breast milk for the first six months of their lives. The sooner the renunciation therapy begins, the less subsequent damage is to be feared.
Prevention
As the exact genesis of fructose intolerance has not yet been clarified, there are no indications for possible preventive measures. It is only possible to avoid potential sequelae of an already diagnosed fructose intolerance (such as deficiency symptoms or irritable bowel syndrome). This requires a well thought-out diet that supplies the body with all the necessary nutrients, but avoids the fructose that triggers symptoms. To this end, a balanced diet plan should be established with a nutrition expert.
Aftercare
Fructose intolerance should always remain under observation. Affected individuals should follow the doctor’s instructions and advice. A person suffering from this condition cannot consume certain foods. For this reason, a food diary is created specifically for the person. In this diary, all the foods that the person should not consume are noted. Special dietary counseling is also a good option for a fructose intolerant person. The professionals, who are perfectly familiar with the diet and intolerances, can best help in this case. It is important that the affected individuals stick to the diet plans that have been put together, otherwise dangerous complications can occur. Bad diarrhea can occur after the consumption of intolerant food. Another quite dangerous complication is allergic reaction. In this one, the patient is in danger of suffocation as the mucous membranes swell and the face flares up. In summary, follow-up care and the associated control of the food consumed should always be adhered to and monitored by the affected person in order to avoid late effects and to alleviate symptoms.
Here’s what you can do yourself
Immediately after diagnosis, patients should seek the advice of a dietitian. This person will provide information on how affected individuals should manage their diet initially and in the long term. In this way, a nutrient deficiency caused by fructose intolerance is prevented. The change in diet is divided into three phases and is documented with the help of a food diary. In the course of the first phase, foods with a high fructose content are to be avoided. It is recommended to avoid apples, pears, mangos, grapes, dried fruits, honey, fruit and vegetable juices. In addition, no foods should be consumed to which household sugar is added. The consumption of chewing gum, sugar-free sweets and diabetic products should also be limited as far as possible. These contain the sugar substitutes xylitol, sorbitol and mannitol, which hinder the absorption of fructose from the intestine. In addition, those affected should not eat any foods that have a flatulent effect. This phase should occupy a time window of two to four weeks and aims to reduce symptoms. The subsequent second phase is classified as a test phase.This should cover a period of six weeks. The focus of this phase is an expansion of the food selection, which should be accompanied by a moderate fructose intake. Consequently, the consumption of tolerated fruits, such as bananas and apricots, must be increased. In addition, it is recommended to eat proportionally more vegetables than fruits. In addition, carbonated beverages, cabbage varieties, citrus fruits and whole grain products should be tested for their tolerance. The goal of the following third phase is the permanent freedom from symptoms of the respective patient. Accordingly, all individually tolerated foods can be consumed in the long term. The long-term diet should be characterized by variety and balance. In addition, sufficient fluid intake must be ensured. Furthermore, new foods should be constantly tested for their individual tolerability, as the absorption of fructose often improves again. Meals should be taken more frequently, but in smaller portions. This relieves both the stomach and the intestines. Furthermore, fruit should not be eaten pure. Accordingly, fruit should be eaten either with a meal, in the form of a dessert, or together with dairy products. The combination of fat and protein leads to a slowed absorption of the fruit sugar.
