Gestational diabetes mellitus (GDM) is a serious problem growing worldwide that needs to be addressed with urgency in consideration of the resulting severe complications for both mother and fetus. Growing evidence indicates that a healthy diet rich in fruit, vegetables, nuts, extra-virgin olive oil and fish has beneficial effects in both the prevention and management of several human diseases and metabolic disorders. In this review, we discuss the latest data concerning the effects of dietary bioactive compounds such as polyphenols and PUFA on the molecular mechanisms regulating glucose homoeostasis. Several studies, mostly based on in vitro and animal models, indicate that dietary polyphenols, mainly flavonoids, positively modulate the insulin signalling pathway by attenuating hyperglycaemia and insulin resistance, reducing inflammatory adipokines, and modifying microRNA (miRNA) profiles. Very few data about the influence of dietary exposure on GDM outcomes are available, although this approach deserves careful consideration. Further investigation, which includes exploring the ‘omics’ world, is needed to better understand the complex interaction between dietary compounds and GDM.

Berries contain vitamin C and are also a rich source of phytochemicals, especially anthocyanins which occur along with other classes of phenolic compounds, including ellagitannins, flavan-3-ols, procyanidins, flavonols and hydroxybenzoate derivatives. This review examines studies with both human subjects and animals on the absorption of these compounds, and their glucuronide, sulphate and methylated metabolites, into the circulatory system from the gastrointestinal tract and the evidence for their localisation within the body in organs such as the brain and eyes. The involvement of the colonic microflora in catabolising dietary flavonoids that pass from the small to the large intestine is discussed along with the potential fate and role of the resultant phenolic acids that can be produced in substantial quantities. The in vitro and in vivo bioactivities of these polyphenol metabolites and catabolites are assessed, and the current evidence for their involvement in the protective effects of dietary polyphenols, within the gastrointestinal tract and other parts of the body to which they are transported by the circulatory system, is reviewed.

Previous cell culture-based studies have shown potential health beneficial effects on gene expression of dietary polyphenols, including those found in red wine and green tea. However, these studies have tended to use higher concentrations (2–100 μm) than those observed in blood (0·1–1 μm) after consuming polyphenol-rich foods or beverages. The present study investigated effects of physiological concentrations of different classes of dietary polyphenol on the expression of genes important in cardiovascular health (endothelial NO synthase (eNOS), endothelin-1 (ET-1) and vascular endothelial growth factor (VEGF)) by cultured vascular endothelial cells (human umbilical vein endothelial cells) in the absence or presence of H2O2. Resveratrol and quercetin (0·1–1 μm) increased eNOS and VEGF mRNA expression particularly in the absence of H2O2 (50 μm) and decreased H2O2-induced ET-1 mRNA expression (P < 0·001 for polyphenol × H2O2 interactions). Similarly, resveratrol and quercetin decreased endothelin secretion into the media, blocking the stimulatory effect of 50 μm-H2O2 (P < 0·001 for polyphenol × H2O2 interaction). Of the nine other polyphenols tested, only epigallocatechin gallate had similar effects on both the eNOS and ET-1 mRNA expression, but to a lesser extent than resveratrol at an equimolar concentration (0·1 μm). The observed effects on gene expression would be expected to result in vasodilation and thereby reduced blood pressure. Since only three of the eleven polyphenols tested had biological activity, it is unclear whether particular structures are important or whether the effects might relate to the relatively high antioxidant capacities of the three active polyphenols.

Platelets play a substantial role in cardiovascular disease, and for many years there has been a search for dietary components that are able to inhibit platelet function and therefore decrease the risk of cardiovascular disease. Platelets can be inhibited by alcohol, dietary fats and some antioxidants, including a group of compounds, the polyphenols, found in fruits and vegetables. A number of these compounds have been shown to inhibit platelet function both in vitro and in vivo. In the present study the effects of the hydroxycinnamates and the flavonoid quercetin on platelet activation and cell signalling in vitro were investigated. The hydroxycinnamates inhibited platelet function, although not at levels that can be achieved in human plasma by dietary intervention. However, quercetin inhibited platelet aggregation at levels lower than those previously reported. Quercetin was also found to inhibit intracellular Ca mobilisation and whole-cell tyrosine protein phosphorylation in platelets, which are both processes essential for platelet activation. The effect of polyphenols on platelet aggregation in vivo was also investigated. Twenty subjects followed a low-polyphenol diet for 3 d before and also during supplementation. All subjects were supplemented with a polyphenol-rich meal every lunchtime for 5 d. Platelet aggregation and plasma flavonols were measured at baseline and after 5 d of dietary supplementation. Total plasma flavonoids increased significantly after the dietary intervention period (P=0·001). However, no significant changes in ex vivo platelet aggregation were observed. Further investigation of the effects of individual polyphenolic compounds on platelet function, both in vitro and in vivo, is required in order to elucidate their role in the relationship between diet and the risk of cardiovascular disease.