What are prebiotics?

Prebiotics are often equated with fiber or confused with probiotics. However, these substances sometimes fulfill very different functions in the human body. This article explains the definition of prebiotics, describes their effects on the human body and introduces foods that are rich in prebiotics.

What are prebiotics?

Prebiotics are carbohydrate molecules, components of plant foods, that cannot be digested. They are therefore neither broken down nor metabolized in the small intestine and thus reach the large intestine intact. There they ferment and serve as food for good intestinal bacteria and promote their proliferation (1).

Prebiotics are selectively utilized by certain microorganisms. They therefore influence the intestinal flora or form metabolic products that can have a positive effect on health (2).

Prebiotics are counted as dietary fiber, but not all dietary fiber is considered prebiotic. Non-prebiotic dietary fiber mainly includes cellulose and hemicellulose. Although these are also part of a healthy diet, they probably have little effect on the intestinal bacteria.

Prebiotics must also be distinguished from probiotics. Probiotics are living microorganisms that can also influence the composition of the intestinal flora and offer health benefits. They are mainly found in fermented foods such as dairy products (yogurt, butter, cheese, curd) (1, 2). Prebiotics serve as a source of nutrients for probiotics and thus promote their growth. Both are therefore important for a healthy intestinal flora. Their combined intake is referred to as synbiotics (3).

What types of prebiotics are there?

Prebiotics are found in many food sources and come in different forms.

The most important types of prebiotics are:

• Inulin and fructooligosaccharides (FOS)
  • Natural components of fruits and vegetables, plants serve to store energy
• Galactooligosaccharides (GOS) and lactulose
  • GOS is a carbohydrate made up of glucose and lactose
  • Lactulose is a synthetic sugar, typically used to treat constipation
• Oligosaccharides in breast milk

Other fibers with prebiotic properties include pectins, beta-glucans and resistant starch. Resistant starch stimulates, among other things, the production of the short-chain fatty acid butyrate. Butyrate, also known as butyric acid, is an important source of energy for colon cells and supports important physiological functions of the body (4, 5).

Potatoes, pasta and rice are popular carbohydrates that are high in starch and are commonly consumed. Cooking or baking these foods creates starch that can be digested and offers little benefit to the gut flora. However, when these foods are cooled after cooking, they create resistant starch, which in turn has prebiotic properties (4).

What sources of prebiotics are there?

As already mentioned, prebiotics are present in numerous foods. The most important representatives are summarized in the table below.

Sources of prebiotics (4)

Prebiotics	source
Inulin and FOS	Chicory roots, blue agave, Jerusalem artichoke, dandelion leaves, garlic, leeks, onions, whole wheat, asparagus, artichokes, barley, rye
GOS	Cow, goat, sheep milk and yoghurt, breast milk, chickpeas, beans, peas, lentils
Lactulose	Synthetic sugar
Pectins	Apples, pears, apricots, citrus fruits
Beta-glucans	Oats, barley, mushrooms, seaweed
Resistant starch	Chickpeas, beans, peas, lentils, oatmeal, cold potatoes, cold pasta, cold rice, barley, green plantains

What is the importance of prebiotics in nutrition?

The effects of prebiotics have been studied in numerous studies. Prebiotics promote the growth of healthy intestinal bacteria, which means that pathogenic or harmful bacteria have less room to spread and their functions are inhibited. A healthy intestinal flora is also said to have a positive effect on other organs in the body (5).

The most important effects of prebiotics include:

• Increase in bacterial mass and stool volume
• Production of short-chain fatty acids: butyrate, acetate, propionate
• Inhibition of the growth of pathogenic germs
• Improved feeling of satiety
• Improve mineral absorption
• Improvement of allergic reactions (2, 4)

How can you incorporate more prebiotic foods into your diet?

In order to maintain a healthy balance of intestinal flora, it is a sensible measure to consume prebiotic foods. Prebiotics are found in numerous foods that are rich in fiber. The foods in the table above, for example, are good sources of prebiotics.

If you take a closer look at these foods, you may notice that consuming some of them can cause digestive problems. Although prebiotics have a positive effect on the body's physiological functions, they can be problematic for people with existing digestive problems. Some of these foods are therefore avoided in the so-called FODMAP diet, which is recommended for symptom relief in irritable bowel syndrome and inflammatory bowel disease.

A FODMAP diet can relieve gastrointestinal complaints, but in the long term it can lead to a reduction in beneficial intestinal bacteria. A daily intake of five to eight grams of FOS and inulin should be enough to achieve positive effects on the intestinal flora without causing unpleasant consequences. To avoid unpleasant side effects, you should approach this amount slowly. By starting with small amounts of selected foods and gradually incorporating more of them into your diet, your body can gradually get used to it (4, 6).

Conclusion

Prebiotics are non-digestible carbohydrates that have a significant impact on the intestinal bacteria and the balance of the intestinal flora in the large intestine. They are found in numerous foods in the form of inulin, fructooligosaccharides, galactooligosaccharides and resistant starch. Significant sources include chicory roots, blue agave, Jerusalem artichoke, garlic, leeks, onions, oats, legumes and milk and yoghurt products. Prebiotics can promote the growth of beneficial intestinal bacteria and fight the harmful ones. This can have a positive effect not only on intestinal health but also on the entire body.

Sources

1. Biesalski HK, Grimm P, Nowitzki-Grimm S. Pocket Atlas of Nutrition. 8th, completely revised edition. Stuttgart, New York: Georg Thieme Verlag; 2020.
2. Matissek R, Hahn A. Food chemistry. 10th, revised and updated edition. Berlin, Heidelberg: Springer Spektrum; 2023.
3. Yadav MK, Kumari I, Singh B, Sharma KK, Tiwari SK. Probiotics, prebiotics and synbiotics: Safe options for next-generation therapeutics. Appl Microbiol Biotechnol 2022; 106(2):505–21. doi: 10.1007/s00253-021-11646-8.
4. Pugliese S. Probiotics and prebiotics – power food for the intestines: With delicious recipes. Munich: Riva; 2018. Available at: https://ebookcentral.proquest.com/lib/kxp/detail.action?docID=5820187.
5. Kaur AP, Bhardwaj S, Dhanjal DS, Nepovimova E, Cruz-Martins N, Kuča K et al. Plant Prebiotics and Their Role in the Amelioration of Diseases. Biomolecules 2021; 11(3). doi: 10.3390/biom11030440.
6. Hills RD, Pontefract BA, Mishcon HR, Black CA, Sutton SC, Theberge CR. Gut Microbiome: Profound Implications for Diet and Disease. Nutrients 2019; 11(7). doi: 10.3390/nu11071613.