| Dietary sources | |
| The enzyme xylose isomerase catalyzes the rearrangement of aldoses to ketoses and vice versa. It is primarily obtained from microorganisms and is mainly used for the production of glucose-fructose syrups from corn starch. The enzyme is not found in foods. | |
| Physiological effects | |
| Intestinal sugar utilization |
|
| Fructose malabsorption |
| Fructose is found in many fruits and vegetables, fruit juices and honey. It is also a component of household sugar (sucrose) and is added to various foods as a sweetener. Intestinal fructose malabsorption is based on a disturbed function of the transport protein GLUT 5 in the mucous membrane of the small intestine, so that fructose supplied with food is not sufficiently absorbed (1). It reaches the lower intestinal sections, where the enzymatic degradation of fructose by intestinal bacteria leads to gas formation and diarrhea. The frequency of intestinal fructose malabsorption is reported to be 36% for Europeans, 50% of whom show clinical symptoms. |
| Enzymatic support of fructose degradation |
| The enzyme xylose isomerase (XI) can convert fructose from food into easily digestible glucose. The dietary intake of XI promotes fructose degradation and reduces the amount of fructose in the small intestine. |
| Depression due to fructose malabsorption |
| Fructose forms complexes with tryptophan in the intestine, resulting in a lack of uptake of this essential amino acid (2). Tryptophan is a key substance for the biosynthesis of the neurotransmitter serotonin, which among other things has an important influence on the mood (“happiness hormone“). This explains why patients with fructose malabsorption have a significantly higher tendency toward depression (3)(4). Increased irritability, restlessness and headaches can also be observed in connection with fructose malabsorption. In addition to the impairment of mood, lowered folic acid and serum zinc levels are also observed. |
| Substrate | Parameter | Reference value | Description |
| Stool | Fructose cleavage activity in stool | > 8.9 g/l | Analysis of bacterial cleavage activity in a stool sample (also possible for sorbitol/xylitol) |
| Breath | H2-Breath test | Difference to initial value < 15 ppm H2 | Hydrogen produced in the intestine during the decomposition of fructose is measured in the exhaled air. |
| Effect on | Symptoms |
| General condition | Headache, agitation, irritability, depression |
| Gastrointestinal system | flatulence, pain, diarrhea (also alternating with constipation) |
| Effect | Indication | Dosing |
| Physiological effects at a low intake |
For targeted degradation of fructose into easily usable glucose in fructose malabsorption | 30 - 100 mg/d |
| General mode of administration | |
| When |
Xylo-isomerase should be taken immediately before a high fructose meal. |
| Side effects | |
| There are no known side effects to date. | |
| Contraindications | |
| There are no known contraindications to date. | |
| Drug or nutrient interactions | |
|
None |
No relevant interactions are known to date. |
| References |
|
(1) Ledochowski M et al. Kohlenhydratmalabsorptionssyndrome. Ernährungsmedizin. Hrsg. Widhalm K, Diallo-Ginstl E, Wien: ÖÄK-Verlag 2000.
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