Photo by http://benvandenbroecke.be/ Copyright, ISAPP 2019.
The concept of a ‘prebiotic’ was put forward in 1995 by Gibson and Roberfroid. Early scientific discussions about prebiotics focused on identifying substances that targeted health-promoting groups of bacteria in the gut: namely, bifidobacteria and lactobacilli.
The current scientific definition of a prebiotic was developed by a panel of experts in microbiology, nutrition, and clinical research convened by ISAPP in 2016. The consensus definition is: “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. Thus, the concept encompasses three crucial parts: a substance, a physiological effect, and a mechanism.
According to this definition, any candidate prebiotic compound must be shown to act as a substrate for gut microorganisms; in addition, its beneficial physiological effect on the host should depend on the use of the compound by microbes. This means a broad range of species or strains may be targeted by a prebiotic substrate—not just bifidobacteria and lactobacilli. However, the prebiotic substance must affect a limited range of microorganisms in the host rather than large swaths of the microbial ecosystem, in order to meet the criterion of being ‘selectively utilized’.
Prebiotic substances may be present in isolated form or in whole foods. The most commonly-studied prebiotics are the soluble fibers inulin, fructooligosaccharides (FOS), galactooligosaccharides (GOS), and more recently human milk oligosaccharides (HMOs). To date, while the prebiotic substances with the most well-documented health effects are forms of dietary fiber, the new definition allows for a broad range of substances targeting different host niches to be considered prebiotics, given appropriate scientific support.
Prebiotic substances have been studied for improving health and therapeutic effects. See these reviews (here and here) for summaries of prebiotic health benefits. At present, there are no official dietary recommendations for ‘adequate intake’ or ‘recommended daily allowance’ for prebiotics in healthy individuals. Most prebiotics for the gut require an oral dose of 3 grams per day or more to confer a benefit. Typically, around 5 grams is the target for FOS and GOS in the daily diet—and this includes plant sources of prebiotics
The recommended daily amount of fiber is 28 g/day, based on 2000 kcal/day diet.