Our knowledge regarding the microbial community that inhabits the human body is expanding at a rapid pace. New worldwide initiatives like sequencing of the human microbiome [1
] along with rapid advances in metabolomics to detect and quantify the products of microbial metabolism [2
] are contributing to a better comprehension of the role of symbionts in health and disease. For instance, activities of the gut microbiota are now known to play a central role in host energy requirements [3
For well over a century, certain microorganisms have been regarded as probiotics, defined recently as “live microorganisms which when administered in adequate amounts confer a health benefit on the host” [4
]. Probiotics are largely administered through functional foods such as dairy products. Lactobacilli and bifidobacteria are currently the most marketed probiotic bacteria worldwide. Prebiotics, or “non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria that can improve the host health”[5
], are an alternative (or adjunct) approach to probiotics and target indigenous beneficial bacteria already established in the gut.
As foods are supplemented with probiotics and new functional ingredients, it is important to understand the beneficial properties of these products and how they aim to improve human health. Here, we explain mechanisms of probiosis and prebiosis and describe how this knowledge can help to design food with improved functionality to target certain populations. Both probiotics and prebiotics have to be consumed regularly to expect to measure the health benefits reported on the related human studies.