What are Prebiotics?

What are Prebiotics?

Etymology: pre- + biotic. 

The word ‘prebiotic’ is composed by the prefix pre-, (“earlier than”, “prior to” or “before”) derived from the Latin prae- (“in front of” or “before”) and the Greek adjective biotic from the noun bios (“life”).

Prebiotic meaning: ‘before life’ or ‘before the advent of life’.

What are the benefits of prebiotics?

Prebiotics may be used as an alternative to probiotics or as supportive agents. Prebiotics are potent gut microbiota modulators, since different prebiotics will stimulate the growth of different microbiota strains. However, these modifications, being individual, strain and species specific, are hard to predict5.

The beneficial effects of prebiotics on human health are numerous, but often hard to associate directly, due to the prebiotic – microbiota – host interaction.

Direct and well-established prebiotic effects are1,6,7: 

• Modulate the colonic microbiota by promoting the increase of specific beneficial bacteria and thus having positive impact on the intestinal microbiota (for example, some prebiotics, like FOS, have been shown to stimulate the growth of endogenous Bifidobacteria)

Indirect effects of prebiotics, mediated by the host gut microbiota, are harder to establish and include1,6,7: 

• Help with digestive problems and prevention of diarrhea or obstipation
• Modulation of the metabolism of the intestinal microbiota
• Cancer prevention
• Positive effects on lipid metabolism
• Prevent vascular disease
• Stimulation of mineral adsorption
• Immunomodulatory properties
• Improve metabolic health and obesity risk
• Help with mental disorders

What are the properties of a prebiotic?

Some of the properties used to classify a compound as prebiotic are4,5:

• Poorly fermented by bacteria in the oral cavity
• Resistant to acidic pH of stomach
• Not hydrolyzed by mammalian enzymes 
• Not digested (or only partially digested)
• Not absorbed in the gastrointestinal tract, namely in the small intestine
• Can be fermented by seemingly beneficial intestinal microbiota
• Poorly fermented by potential pathogens in the bowel
• The growth and/or activity of the intestinal microbiota can be selectively stimulated by this compound and this process improves host’s health

What are the mechanisms of action of prebiotics?

The microorganisms within our gut can digest the fiber that we, as humans, cannot. This fiber is a source of energy, nutrients and vitamins to these microscopic organisms. When digesting these fibers, bacteria in the gut produce short-chain fatty acids (SCFAs), which are the main products of prebiotic degradation and the main energy source of colonocytes, the cells lining the colon, making them crucial to gastrointestinal health. 

Why are SCFAs important?

SCFAs are considered the end products of fermentation of dietary fibers by the anaerobic intestinal microbiota and have been shown to exert multiple beneficial effects on mammalian energy metabolism8. These molecules are small enough to diffuse through gut enterocytes and enter blood circulation, affecting not only the gastrointestinal tract but also other distant site organs and systems. Therefore, prebiotics, mainly through SFCAs, exert their protective effect not only on the GI system but also on other parts of the body, such as the central nervous system, immune system, and cardiovascular system6. SCFAs have been associated with reduced risk of inflammatory and metabolic diseases, such as obesity, type 2 diabetes, and heart disease, among others6. 

Types of Prebiotics

There are many types of prebiotics, most of them are a subset of carbohydrate groups: oligosaccharides and polysaccharides. Different authors suggest different categories or types of prebiotics, a simple classification can be found on the table below6,9,10:

• Prebiotic foods

For humans, the type of birth has major importance in the composition of GI tract microbiota in the beginning of life, and after that, the type of feeding becomes crucial. Human milk is the first and perfectly balanced prebiotic for a newborn. The Human Milk Oligosaccharides (HMOs), found in human breast milk, selectively feed certain strains of Bifidobacteria within the infant’s developing digestive tract. These compounds have complex structures and are unique to breast milk10. According to a 2006 article, “breast-fed infants show a predominance of Bifidobacteria and Lactobacilli, whereas bottle-fed infants develop a mixed flora with a lower number of Bifidobacteria11.”  The authors highlight that “the ‘bifidogenic effect’ of human milk is not related to a single growth-promoting substance, but rather to a complex of interacting factors11.” This is one of the main reasons why breastfeeding is so important and irreplaceable. There is no way to mimic the complexity and perfect balance of human milk.

After being breastfed, it is essential for the health of the microbiome and the human that we continue feeding these gut microbes with beneficial foods. The type and quality of food we eat daily has an enormous effect on gut microbiota. The chemical residues and pesticides found in non-organic foods, along with cycles of antibiotics are among the factors that disrupt the balance in the gut bacteria. Knowing that the environment and lifestyle have a huge impact on the health of your gut, and that some of those factors are out of your control, one of the things you can easily implement in your life is a diet rich in whole food prebiotics. 

What whole foods are rich in prebiotics? 

Prebiotics are present mostly in carbohydrates rich in fiber, such as certain fruits, vegetables, and whole grains. Fiber is not digestible by humans and passes through the digestive tract undigested and then feeds the beneficial bacteria in the human gut. That is the reason why fiber can be considered the most central prebiotic for humans.

Below you find a list of whole foods rich in prebiotics and the type of prebiotic associated with them.

Best Natural Whole Food Sources of Prebiotics Important

Remember, prebiotics play an essential role in human health, so try to include at least one prebiotic rich food in each of your meals. Since the fiber content of some of these foods may be altered during cooking, it is better to eat them raw if you can.

References

1. Gibson GR, Roberfroid MB. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J Nutr. 1995 Jun;125(6):1401-12. doi: 10.1093/jn/125.6.1401. PMID: 7782892.
2. Pineiro, Maya & Asp, Nils-Georg & Reid, Gregor & Macfarlane, Sandra & Morelli, Lorenzo & Brunser, Oscar & Tuohy, Kieran. (2008). FAO Technical Meeting on Prebiotics. Journal of clinical gastroenterology. 42 Suppl 3 Pt 2. S156-9. 10.1097/MCG.0b013e31817f184e.
3. Food and Agriculture Organization. FAO Technical Meeting on Prebiotics: Food Quality and Standards Service (AGNS), Food and Agriculture Organization of the United Nations (FAO) FAO; Rome, Italy: Sep 15–16, 2007. FAO Technical Meeting Report.
4. Gibson G.R., Scott K.P., Rastall R.A., Tuohy K.M., Hotchkiss A., Dubert-Ferrandon A., Gareau M., Murphy E.F., Saulnier D., Loh G., et al. Dietary prebiotics: Current status and new definition. Food Sci. Technol. Bull. Funct. Foods. 2010;7:1–19. doi: 10.1616/1476-2137.15880.
5. Markowiak P, Śliżewska K. Effects of Probiotics, Prebiotics, and Synbiotics on Human Health. Nutrients. 2017 Sep 15;9(9):1021. doi: 10.3390/nu9091021. PMID: 28914794; PMCID: PMC5622781.
6. Davani-Davari D, Negahdaripour M, Karimzadeh I, Seifan M, Mohkam M, Masoumi SJ, Berenjian A, Ghasemi Y. Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications. Foods. 2019 Mar 9;8(3):92. doi: 10.3390/foods8030092. PMID: 30857316; PMCID: PMC6463098.
7. de Vrese M., Schrezenmeir J. (2008) Probiotics, Prebiotics, and Synbiotics. In: Stahl U., Donalies U.E., Nevoigt E. (eds) Food Biotechnology. Advances in Biochemical Engineering/Biotechnology, vol 111. Springer, Berlin, Heidelberg. https://doi.org/10.1007/10_2008_097
8. den Besten G, van Eunen K, Groen AK, Venema K, Reijngoud DJ, Bakker BM. The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. J Lipid Res. 2013 Sep;54(9):2325-40. doi: 10.1194/jlr.R036012. Epub 2013 Jul 2. PMID: 23821742; PMCID: PMC3735932.
9. Ailioaie LM, Litscher G. Probiotics, Photobiomodulation, and Disease Management: Controversies and Challenges. Int J Mol Sci. 2021 May 6;22(9):4942. doi: 10.3390/ijms22094942. PMID: 34066560; PMCID: PMC8124384.
10. https://www.prebiotics.com/types-of-prebiotics, accessed June 29, 2021
11. Coppa GV, Zampini L, Galeazzi T, Gabrielli O. Prebiotics in human milk: a review. Dig Liver Dis. 2006 Dec;38 Suppl 2:S291-4. doi: 10.1016/S1590-8658(07)60013-9. PMID: 17259094.