Microbiota and dietary interactions: an update to the hygiene hypothesis?

The dramatic increase in the incidence and severity of allergy and asthma has been proposed to be linked with an altered exposure to, and colonization by, micro-organisms, particularly early in life. However, other lifestyle factors such as diet and physical activity are also thought to be important, and it is likely that multiple environmental factors with currently unrecognized interactions contribute to the atopic state. This review will focus on the potential role of microbial metabolites in immunoregulatory functions and highlights the known molecular mechanisms, which may mediate the interactions between diet, microbiota, and protection from allergy and asthma.