The role of (poly)phenolic compounds as components responsible for the protective effects of a fruit and vegetable-rich diet has become an important area of nutrition research. Unlike vitamins, they are not essential for well-being, but there is increasing evidence that modest long-term intakes can have favourable effects on the incidence of chronic diseases, including type II diabetes and its various complications. However, (poly)phenols appear in the circulatory system not as the parent compounds but as phase II metabolites, and their presence in plasma after dietary intake rarely exceeds nM concentrations. The majority passes to the colon where they are degraded by the local microbiota to small phenolic acids, which are then absorbed. Whilst most of the published papers on (poly)phenol bioactivity still describe the effects of molecules that are only present in planta, we have carried out innovative and detailed studies applying polyphenolic metabolites to establish reasonable mechanisms through which some candidates in this immense class of plant secondary metabolites may exert beneficial actions toward the pathological processes leading to the onset of diabetes and its complications. Among these mechanisms, this lecture will discuss the ability to increase insulin secretion, anti-glycative and anti-inflammatory activities and perturbation of some other cellular pathways potentially involved in the complex series of events gravitating around glucose intolerance.