Prebiotics are substances that induce the growth or activity of microorganisms (e.g., bacteria and fungi) that contribute to the well-being of their host. The most common example is in the gastrointestinal tract, where prebiotics can alter the composition of organisms in the gut microbiome. However, in principle it is a more general term that can refer to other areas of the body as well. For example, certain hand moisturizers have been proposed to act like prebiotics to improve the activity or composition of skin microbiota.
In diet, prebiotics are typically non-digestible fiber compounds that pass undigested through the upper part of the gastrointestinal tract and stimulate the growth or activity of advantageous bacteria that colonize the large bowel by acting as substrate for them. They were first identified and named by Marcel Roberfroid in 1995. As a functional food component, prebiotics, like probiotics, are conceptually intermediate between foods and drugs. Depending on the jurisdiction, they typically receive an intermediate level of regulatory scrutiny, in particular of the health claims made concerning them.
Roberfroid offered a refined definition in the March 2007 Journal of Nutrition stating: "A prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health."
Additionally, in his 2007 revisit of prebiotics, Roberfroid stated that only two particular prebiotics then fully met this definition: trans-galactooligosaccharide and inulin. Other dietary fibers also fit the definition of prebiotics as developed by Roberfroid such as Larch arabinogalactin (LAG), resistant starch, pectin, beta-glucans, and Xylooligosaccharides (XOS).
The prebiotic definition does not emphasize a specific bacterial group. Generally, however, it is assumed that a prebiotic should increase the number or activity of bifidobacteria and lactic acid bacteria. The importance of the bifidobacteria and the lactic acid bacteria (LABs) is that these groups of bacteria may have several beneficial effects on the host, especially in terms of improving digestion (including enhancing mineral absorption) and the effectiveness and intrinsic strength of the immune system. A product that stimulates bifidobacteria is considered a bifidogenic factor. Some prebiotics may thus also act as a bifidogenic factor and vice versa, but the two concepts are not identical.
|Top 10 Foods Containing Prebiotics|
|Food||Prebiotic Fiber Content by Weight|
|Raw, Dry Chicory Root||64.6%|
|Raw, Dry Jerusalem Artichoke||31.5%|
|Raw, Dry Dandelion Greens||24.3%|
|Raw, Dry Garlic||17.5%|
|Raw, Dry Leek||11.7%|
|Raw, Dry Onion||8.6%|
|Raw Wheat bran||5%|
|Whole Wheat flour, Cooked||4.8%|
While there is no broad consensus on an ideal daily serving of prebiotics, recommendations typically range from 4 to 8 grams (0.14–0.28 oz) for general digestive health support, to 15 grams (0.53 oz) or more for those with active digestive disorders. Given an average 6 grams (0.21 oz) serving, below are the amounts of prebiotic foods required to achieve a daily serving of prebiotic fiber:
|Food||Amount of food to achieve 6 g serving of prebiotics|
|Raw Chicory Root||9.3 g (0.33 oz)|
|Raw Jerusalem Artichoke||19 g (0.67 oz)|
|Raw Dandelion Greens||24.7 g (0.87 oz)|
|Raw Garlic||34.3 g (1.21 oz)|
|Raw Leek||51.3 g (1.81 oz)|
|Raw Onion||69.8 g (2.46 oz)|
|Cooked Onion||120 g (4.2 oz)|
|Raw Asparagus||120 g (4.2 oz)|
|Raw Wheat Bran||120 g (4.2 oz)|
|Whole Wheat Flour, Cooked||125 g (4.4 oz)|
|Raw Banana||600 g (1.3 lb)|
Preliminary research has demonstrated potential effects on calcium and other mineral absorption, immune system effectiveness, bowel acidity, reduction of colorectal cancer risk, inflammatory bowel disease (Crohn's disease or ulcerative colitis) hypertension and defecation frequency. Prebiotics may be effective in decreasing the number of infectious episodes needing antibiotics and the total number of infections in children aged 0–24 months.
While research demonstrates that prebiotics lead to increased production of short-chain fatty acids (SCFA), more research is required to establish a direct causal connection. Prebiotics may be beneficial to inflammatory bowel disease or Crohn's disease through production of SCFA as nourishment for colonic walls, and mitigation of ulcerative colitis symptoms.
The immediate addition of substantial quantities of prebiotics to the diet may result in an increase in fermentation, leading to increased gas production, bloating or bowel movement. Production of SCFA and fermentation quality are reduced during long-term diets of low fiber intake. Until bacterial flora are gradually established to rehabilitate or restore intestinal bacteria, nutrient absorption may be impaired and colonic transit time temporarily increased with an immediate addition of higher prebiotic intake.
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Presently there are only 2 food ingredients that fulfill these criteria, i.e., inulin and trans-galactooligosaccharides (TOS).
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