Writing in the academic journal Trends in Food Science & Technology, a team of Danish scientists said that until now the field of prebiotic research has been “characterized by a one-view-fits-all approach, implicating that if a putatively prebiotic compound is good for something, it is good for everything.”
However, one area where this implication has been proved lacking, they said, is when it comes to the supposed preventive effect of prebiotics against intestinal pathogens.
Led by Professor Tine Rask Licht, of the Technical University of Denmark, the reviewers noted that “although indeed most evidence on effects of prebiotics against infections is positive, some studies indicate that prebiotic carbohydrates cause increased susceptibility to specific gastrointestinal infections.”
“It is therefore important to facilitate the scientific community’s access also to the body of knowledge constituted by negative trials,” they added.
“Still, we believe that there is consistent evidence that specific prebiotics has the potential to prevent specific intestinal infections,” they explained; noting that whilst the measured effects are generally not overwhelmingly large “it is important to remember that prebiotics are to be considered as food – not drugs.”
“The notion that one of the most important functions of the intestinal microbiota is to protect the host organism from colonization by ingested pathogens is not new ... and is based on the idea that any new bacterium introduced into the gut will have to compete with the established microbiota for available ecological niches (nutrients, adhesion sites) in order to persist in the intestine,” explained Rask Licht and her colleagues.
However, they noted that research has also suggested that intestinal bacteria may also contribute resistance through immune stimulation, including production of specific antimicrobial substances (bacteriocins), and through release of metabolic products such as short-chained fatty acids which lower the gut pH to levels below those optimal for growth of pathogens and improves epithelial and immune defence mechanisms.
“Several dietary fibers, including several fibers possessing prebiotic properties, have been shown to hold immune modulating activities, both in in vitro and in vivo studies,” they noted; adding that recent research that screened a high number of dietary fibres revealed that “some prebiotics, but not all, could stimulate and modulate the response of dendritic cells to LPS.”
Speaking with NutraIngredients in a previous exclusive interview, Rask Licht said that one of the real challenges with proving the effects of functional ingredients such as prebiotics lies in being able to measure if, and how healthy people become healthier.
The research team added that the fact that direct health benefits of microbiota modulation may be difficult to measure using the currently accepted health markers “does not imply that effects of prebiotics on commensal microbes are not beneficial.”
“Rather, it illustrates our current lack of knowledge on the role of gut microbiota and prebiotics on host health in general ... The role of the gut microbiota on host health is increasingly appreciated, but the exact mechanisms behind the host–microbial interactions are not yet well understood,” they said.
However, Rask Licht said that as the science in the area moves forward and “begins to capture the attention it deserves, these mechanisms will be gradually revealed, which in turn will benefit the future of functional food ingredients.”
NutraIngredients previous exclusive interview with Professor Rask Licht can be found here.
Source: Trends in Food Science & Technology
Published online ahead of print, doi: 10.1016/j.tifs.2011.08.011
“Prebiotics for prevention of gut infections”
Authors: T. Rask Licht, T. Ebersbach, H. Frøkiær