Prebiotics

Prebiotics are substrates that promote the growth of bacteria. They are thus essential for a balanced microbiota.

Prebiotics are non-digestible, yet essential fibers in the diet that selectively stimulate the growth of microbiota bacteria¹,² in the colon. Contrary to simple or refined sugars supplied by the diet and digested, these prebiotics are not assimilated by the body, but are broken down via fermentation in the colon intestinal flora bacteria. 

What are they?

The best-studied are fructooligosaccharides (FOS), inulin, and galactooligosaccharides. The first are found in many foods - garlic, onions, bananas, and asparagus - and also in whole grain wheat, rye, and barley. Inulin is found in chicory roots and artichokes. As for galactooligosaccharides (GOS), they are found in fermented milk products like yogurt, as well as in breast milk. Diet remains the only source of prebiotics, and it should be sufficiently diverse to preserve the microbiota equilibrium.

Benefits

Beyond an increase in the number of bifidobacteria, prebiotics also positively influence other parameters. They notably increase the absorption of magnesium³,⁴ and reduce blood lipids⁵. Furthermore, studies seem to show a benefit by reducing the formation of colorectal polyps that can lead to cancer⁶,⁷ or food allergies⁸.

Sources:

1. Joanne Slavin. Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients 2013 Apr; 5 (4): 1417–1435. http://www.mdpi.com/2072-6643/5/4/1417
2. Gibson GR et al. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J Nutr. 1995; 125(6): 1401-12.  https://www.ncbi.nlm.nih.gov/pubmed/7782892
3. Van den Heuvel EG et al. Short-chain fructo-oligosaccharides improve magnesium absorption in adolescent girls with a low calcium intake. Nutr Res. 2009; 29(4): 229-37. https://www.ncbi.nlm.nih.gov/pubmed/19410973
4. Tahiri M et al. Five-week intake of short-chain fructo-oligosaccharides increases intestinal absorption and status of magnesium in postmenopausal women. J Bone Miner Res. 2001; 16(11): 2152-60. https://www.ncbi.nlm.nih.gov/pubmed/11697813
5. Slavin JL. Position of the American Dietetic Association: health implications of dietary fiber. J Am Diet Assoc. 2008; 108(10): 1716-31. https://www.ncbi.nlm.nih.gov/pubmed/18953766
6. Buddington KK et al. Dietary Oligofructose and Inulin Protect Mice from Enteric and Systemic Pathogens and Tumor Inducers. J. Nutr 2002; 132: 472. https://www.ncbi.nlm.nih.gov/pubmed/11880573
7. Rafter J et al. Dietary synbiotics reduce cancer risk factors in polypectomized and colon cancer patients. Am J Clin Nutr 2007; 85: 488–96. https://www.ncbi.nlm.nih.gov/pubmed/17284748
8. Bouchaud G. et al. Maternal exposure to GOS/inulin mixture prevents food allergies and promotes tolerance in offspring in mice. Allergy 2016; 71(1):68-76 https://www.ncbi.nlm.nih.gov/pubmed/26424001

Additional Source:

http://www.med.monash.edu.au/cecs/gastro/prebiotic/faq/