[1] The most common environment concerning their effects on human health is the gastrointestinal tract, where prebiotics can alter the composition of organisms in the gut microbiome.
Dietary prebiotics are typically nondigestible fiber compounds that pass undigested through the upper part of the gastrointestinal tract and help growth or activity of advantageous bacteria in the colon by acting as substrates for them.
Common prebiotics used in food manufacturing include beta-glucan from oats, resistant starch from grains and beans, and inulin from chicory root.
[3] In its earliest definition, the term prebiotics was used to refer to non-digestible food ingredients that were beneficial to the host through their selective stimulation of specific bacteria within the colon.
[7] Based on the previous classifications, plant-derived carbohydrate compounds called oligosaccharides as well as resistant starch are the main source of prebiotics that have been identified.
[8][4][9][10] Specifically, fructans and galactans are two oligosaccharide sources which have been found to stimulate the activity and growth of beneficial bacterial colonies in the gut.
[3][4][18] With improved mechanistic techniques in recent years, the current prebiotic targets have expanded to a wider range of microbes, including Roseburia spp., Eubacterium spp., Akkermansia spp., Christensenella spp., Propionibacterium spp.
For instance, oats and barley have high amounts of beta-glucans, fruit and berries contain pectins, seeds contain gums, onions and Jerusalem artichokes are rich in inulin and oligofructose, and bananas and legumes contain resistant starch.
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: Preliminary research has demonstrated potential effects on calcium and other mineral absorption,[29] immune system effectiveness,[30][31] bowel acidity, reduction of colorectal cancer risk,[32] inflammatory bowel disease (Crohn's disease or ulcerative colitis),[33] hypertension[34] and defecation frequency.
[41] Until bacterial flora are gradually established to rehabilitate or restore intestinal bacteria, nutrient absorption may be impaired and colonic transit time temporarily increased with a rapid addition of higher prebiotic intake.