Prebiotics Explained Simply

1. What It Is About

Prebiotics are indigestible components of food. They are utilised by bacteria in the large intestine. In doing so, they favour certain microorganisms. Important: prebiotics are not a single substance but an entire class of compounds. This includes, for example, galacto-oligosaccharides, fructo-oligosaccharides, inulin and lactulose. Some occur naturally in foods, but only in small amounts. Therefore attempts are made to produce them industrially 7. During breakdown, short-chain fatty acids are formed. These enter the blood and can also influence organs far from the intestine 7. Reviews also describe how prebiotics act on the immune system of the intestinal mucosa 8 and how they connect with the brain via the gut-brain axis 9. In studies, prebiotics are used in different ways: sometimes as a single substance, sometimes as a mixture, sometimes together with probiotics. Probiotics are living microorganisms; prebiotics, by contrast, are their food. This combination is called a synbiotic 6.

2. What Studies Show

The findings are clearest where only prebiotics were tested. Most controlled human studies concern the intestine and the gut flora. Preterm infants: an analysis of 18 studies with 1322 preterm infants examined prebiotics alone. The children developed sepsis less often, died less often and spent less time in hospital. The time until full feeding via tube was also shorter. No difference was found for a severe intestinal inflammation, necrotising enterocolitis 1. Women with polycystic ovary syndrome: this is a hormonal disorder in which, among other things, the cycle is irregular. An analysis of 20 studies with 1271 women tested prebiotics alone or as part of synbiotics. Body-mass index and diastolic blood pressure decreased. For other values such as waist circumference or blood glucose, the certainty of the findings was lower 2. Constipation: an analysis of 5 studies with 199 affected individuals tested prebiotics and synbiotics. It found that bowel movements became more frequent and stool consistency improved. The number of studies was small; the finding is an indication 5. Inflammatory markers: a large analysis of 90 studies with 5207 children and adults tested prebiotics and synbiotics. It found lower inflammatory markers in the blood. Such values are measurement parameters, not proof that a disease occurs less often 3. Gut flora: an analysis of prebiotics, probiotics and synbiotics in older people showed that the number of bifidobacteria increased markedly. Bifidobacteria are considered beneficial gut bacteria 4.

3. What Remains Unclear

Many studies do not test prebiotics alone. They administer prebiotics and probiotics together. It is then impossible to say which part produced the effect. This applies to a large proportion of the work, for example on liver values, allergies or vaccine responses. In addition, prebiotics are not a uniform substance. The studies differ in the preparation and in what was measured. Some measure gut flora in stool, others inflammatory markers, others questionnaires on mood or appetite. A changed measurement value is not the same as a better disease course. The most cited works in the field are reviews and consensus papers, not original studies. The definition of what constitutes a synbiotic was established in a consensus paper 6. How prebiotics affect diseases in the long term remains to be clarified.

4. What This Means in Everyday Life

Anyone reading about prebiotics should ask three questions: which substance was tested? In what form? And what was measured? An example: a study can show that inflammatory markers in the blood change. This is an indication of a process in the body. It does not automatically mean that people feel less ill or fall ill less often. A second example: in constipation it was observed that bowel movements became more frequent. This is something that those affected notice directly. Such findings are more tangible than a laboratory value. And a third: when prebiotics and probiotics were given together, it remains open which part is effective. Such results say little about prebiotics alone. Prebiotics are therefore not a single thing with a single effect. What a particular preparation achieves depends on the substance, the preparation and the person.

All Details with Study Numbers and Sources: detailed page on prebiotics. For children: prebiotics for children.