Unlike probiotics, which are defined living microorganisms, prebiotics are indigestible carbohydrates such as fructose and lactose oligosaccharide. Prebiotics stimulate the growth and activity of bifidobacteria and lactobacillus, in other words the beneficial bacteria of the intestinal flora.
The intestine of an adult human contains approximately 1014 bacteria of more than 400 different species and sub-species, which together weigh between 1 - 1.5 kg. In the large intestine, we can differentiate between beneficial bacteria such as bifidobacteria and lactobacillus, and facultative pathogenic bacteria such as E. coli, salmonella and clostridium.
Beneficial functions of the physiological intestinal flora include:
Growth inhibition of pathogenic bacteria
Immunomodulating activity
Restoration of intestinal flora after antibiotic treatment therapy
Lactulose is a synthetically manufactured disaccharide with a prebiotic effect made from fructose and galactose. Prebiotic oligosaccharides occur naturally in plants such as garlic, asparagus, and onions but also in yoghurt and milk.
Bacteria which are foreign to the large intestine generally cannot become established for longer periods there. The suitable method of prophylactically and therapeutically acting against the establishment of such bacteria in the intestine therefore involves physiologically promoting the existing intestinal flora adapted to the human body. Clear changes in the intestinal flora can be achieved using lactulose even after use has been discontinued. As a result, the production of short-chained fatty acids increases, the emergence of potentially toxic aromates is prevented, and bacterial urease activity and therefore also ammonia production decrease. These changes have a clearly positive influence on this environment and act against a possible toxicity of intestinal contents (e. g., in the treatment of portosystemic encephalopathy). In addition to suppressing the potentially pathogenic bacteria E. coli, clostridium and salmonella through bifidobacteria, lactulose is also involved in the reduction of yersinia, shigella and rota viruses. The same can be shown for candida albicans.
The prebiotic effect of lactulose appears to have a positive influence on a series of illnesses whose pathogenesis involve disrupted intestinal bacterial flora and its consequences. Among the potential uses of prebiotics are the treatment of inflammatory intestinal diseases, as well as the prevention of gallstones and intestinal infections. This is supported by the results of pre-clinical studies; controlled studies with patients have yet to be carried out. Another important protective effect appears to involve the emergence of colon karzinomes. These indications must also be confirmed by further studies.
There are also indications that lactulose has a positive effect in cases of atopy. By administering the probiotic rhamnosus strain of lactobacillus, it was possible to reduce the incidence of atopic eczema in susceptible children during the two years after birth. In a further test, a lower rate of establishment of bifidobacteria and lactobacillus was found in the intestinal flora of children who suffer from allergies. Problems in the microbiological intestinal flora therefore appear to have a negative influence on the activity of the body’s immune system. By giving probiotics such as lactobacillus, it was possible to improve existing loss of balance and increase immunomodulating activity. However, further studies are required to confirm the assumption that the intestinal flora can be improved through an increase in the growth of lactobacillus solely as a result of administering lactulose.
As long as prebiotics are not fermented they act osmotically: Water is absorbed into the intestinal lumen and faeces increases in volume. This stimulates intestinal motility and bowel motion is speeded up. This is why lactulose is given for the treatment of obstipation. In the intestine, lactulose is converted into short-chained fatty acids. This lowers the pH value, thus promoting the growth of bifidobacteria.
Lactulose reduces the presence of ammonia in the intestine by, on the one hand, the conversion of NH3 to NH4+ which low pH values promote, and, on the other hand, by suppressing ammonia-forming bacteria through bifidobacteria or lactobacillus. The fact that ammonia has a toxic effect on the brain explains the effect of lactulose as a therapeutic agent in cases of hepatic encephalopathy.
You will find more detailed information on obstipation and portosystemic (hepatic) encephalopathy in the Chapter PSE on this website.
Prebiotics increase intestinal gas production and theoretically there is risk of increased diarrhoea. Patients with irritable bowel syndrome do not tolerate prebiotics well. However, lower doses of prebiotics are usually completely unproblematic. For this reason children and pregnant women can safely take lactulose in appropriately reduced doses.
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