Harvard Medical School Division of Nutrition

Glenn Gibson, M.D.
Professor of Food Microbiology
University of Reading, United Kingdom

What are Prebiotics and How do They Function?

The human large intestine is an intensively colonized area containing bacteria that are health positive, as well as pathogenic. This has led to functional food developments that fortify the former at the expense of the latter. Probiotics have a long history of use in humans as live microbial feed additions. In contrast, a prebiotic is a non-digestible food ingredient that beneficially affects the host by targeting indigenous components thought to be positive. Main prebiotic targets at the moment are bifidobacteria and lactobacilli (although this may change as our knowledge of the flora diversity and functionality expands). Any dietary component that reaches the colon intact is a potential prebiotic, however much of the interest in the development of prebiotics is aimed at non-digestible oligosaccharides such as inulin type fructooligosaccharides (FOS) and trans-galactooligosaccharides (TOS). In Europe, FOS and TOS have been shown to be prebiotics, through numerous volunteer trials, as evidence by their ability to positively change the gut flora composition after a short feeding period. Other prebiotics are emerging. Some prebiotics occur naturally in several foods such as leek, asparagus, chicory, Jerusalem artichoke, garlic, artichoke, onion, wheat, banana and oats. However, these foods contain only trace levels, so developments have taken the approach of removing the active ingredients from such sources and adding them to more frequently consumed products in order to attain levels whereby a prebiotic effect may occur, e.g. cereals, confectionery, biscuits, infant feeds, yoghurts, table spreads, bread, sauces, drinks, etc.

If progress in the use of dietary intervention directed towards particular gut bacteria is to be exploited, a sound research base is required. Some areas of interest may include:

• the application of advanced molecular procedures that help identify the gut microbial diversity as well as allow effective tracking of microflora changes in response to diet
• the prebiotic potential of dietary ingredients and an identification of those foodstuffs that can be fortified
• whether certain target groups are more susceptible to the approach (elderly, weaning stage, formula-fed infants, hospitalized patients)
• a determination of the health consequences that are associated with gut flora modulation (e.g. anti-pathogen activities, reduced inflammatory disorders, immunological effects, protective aspects for bowel cancer, neutralization of certain toxins)
• interaction of the gut microbiota with the host at a metabolic level

This presentation will discuss the prebiotic concept and overview the generation of new trans-galactooligosaacharide that has been tested in various human studies.