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Fructose malabsorption

Besides fructose intolerance (fructose metabolic disorder, HFI), fructose absorption problems can also cause a fructose intolerance. This malabsorption may develop following damage to the epithelium of the small intestine due to a HFI, but also relatively often manifests independently of an HFI. With this intolerance referred to as fructose malabsorption, the transport capacity of the transport protein GLUT5 in the mucous membrane of the small intestine is restricted, whereby the fructose in the small intestine is insufficiently absorbed.

The fructose that thereby floods into the colon is decomposed by bacteria. The resulting fermentation products (CO2, methane, short-chain fatty acids, H2) cause symptoms such as bloating, flatulence, and cramping stomach pain. The fructose molecules are osmotically active and therefore in many cases cause diarrhoea.
Since the hydrogen H2 formed during the fructose fermentation reaches the lungs via the bloodstream, fructose malabsorption can be diagnosed by means of a H2 breath test (fructose load test). 

Diagnostic in case of fructose malabsorption

 

Since the hydrogen H2 formed during the fructose fermentation reaches the lungs via the bloodstream, fructose malabsorption can be diagnosed by means of a H2 breath test (fructose load test).

 

Cave:
Before carrying out a fructose load test, HFI must first be ruled out (fructose intolerance gene test) because a fructose load can bring about life-threatening metabolic crises in affected patients.

 

 

Therapy

Whereas HFI patients therefore have to eat a virtually fructose-free diet for life, in the case of those with fructose malabsorption, a completely fructose-free diet leads to a deterioration in the long term, as the fructose transport modules in the small intestine are further reduced with abstinence from fructose. With fructose malabsorption, therefore, a fructose-modified diet with increased proportions of fat and protein is selected, which increases the expression of the transport proteins and therefore the fructose absorption in the small intestine. Sorbitol should be avoided due to its blocking property of Glut-5-transporter.
Essentially, in case of those with fructose malabsorption, it must be remembered that many diabetic products, dietary supplements, and calorie-reduced foods contain sorbitol. As fructose is produced when sorbitol is broken down, ingesting these products worsens the symptoms.

Patients with fructose malabsorption have a significantly higher predisposition to depression.

As with irritable bowel syndrome, in patients with fructose malabsorption also, psychological changes can often be observed. Studies show that the malabsorption of fructose is associated with significantly higher depression scores in comparison with people who have a normal fructose absorption capacity. This is caused by a chronic depletion of tryptophan due to the fructose deposited in the intestine.

Fructose malabsorption inhibits the absorption of tryptophan

The fructose deposited (not absorbed) in the intestine binds to the tryptophan from the food and blocks its absorption. An insufficient supply of tryptophan causes a reduction in the synthesis of serotonin, leading to symptoms of depression and the symptom of "sweet cravings". Studies have shown that a fructose-reduced diet can improve early signs of depression.

Vitamin deficiency and trace element deficiency with fructose malabsorption

Patients with fructose malabsorption show significantly lower levels of folic acid, among others. A significant link to fructose malabsorption has also been shown for zinc deficiency conditions. It is therefore recommended for patients with fructose malabsorption to monitor the trace element balance by means of multi-element analysis. This means that deficiencies can be detected early and specific substitutions made. You can find detailed information on the mineral profile.

Literature

  • Ledochowski et al. (2005): Fruktosemalabsorption. Ernährung/Nutrition. 29(4).
  • Ledochowski et al. (2000): Fructose-and Sorbitol-reduced Diet improves Mood and Gastrointestinal Disturbance in Fructose Malabsorbers. Scand J Gastroenterol. 35(10):10148-52.