The number of patients with allergic and inflammatory disorders has been increasing during the past several decades. Accumulating evidence has refined our understanding of the relationship between allergic diseases and the gut microbiome. In addition, the gut microbiome is now known to produce both useful and harmful metabolites from dietary materials. These metabolites and bacterial components help to regulate host immune responses and potentially affect the development of allergic diseases. Here, we describe recent findings regarding the immunologic crosstalk between commensal bacteria and dietary components in the regulation of host immunity and the influence of this relationship on the development of allergic diseases.