Could gestational diabetes mellitus be managed through dietary bioactive compounds? Current knowledge and future perspectives.

Gestational diabetes mellitus (GDM) is the most common metabolic disorder during pregnancy( 1 ), and its prevalence is increasing worldwide( 2 ). Women with GDM are at a high risk of developing type 2 diabetes (T2D) later in life( 1 ); in addition, the higher baseline BMI and weight gain often found after GDM occurrence increase the risk of progression from GDM to T2D( 3 ). Moreover, uncontrolled GDM is associated with a detrimental intra-uterine environment, which leads to fetal complications and an increased risk for the child of developing obesity and metabolic disorders( 4 , 5 ). In response to the marked rise in GDM, it is of paramount importance to identify appropriate treatments to prevent maternal and fetal complications associated with this disease. At present, the management of GDM is a big challenge because of its heterogeneity (i.e. ethnic as well as intra-, and inter-country differences)( 2 , 6 , 7 ), and the incomplete knowledge of its pathophysiology( 8 ). As a result, standardised guidelines for GDM are difficult to arrive at worldwide, as are the intervention strategies aimed at preventing or/and reducing the burden of this disorder. In addition, obesity and maternal overweight have been considered as the main risk factors for GDM( 1 ); the reduction of these risk factors is essential for the well-being of mother and offspring( 5 ). Pre-pregnancy and early pregnancy are the best periods for a dietary intervention to control weight in order to prevent the long-lasting effects of maternal diabetes or obesity( 9 ). There is increasing evidence that the dietary patterns having beneficial effects both in prevention and management of diabetes are characterised by high consumption of plant foods (e.g. whole grains, fruit, vegetables and extra-virgin olive oil, nuts) and fish, and low consumption of animal-based, high-fat, processed foods, that is, the Mediterranean-style diet (MedDiet)( 10 ). The MedDiet is a primarily plant-based dietary pattern that has been strongly associated with lower incidence of CVD, and neoplastic diseases, and an overall reduced mortality( 11 , 12 ). Adherence to the MedDiet correlates with better glycaemic control, a reduced risk of both total and cardiovascular mortality in diabetic subjects in Mediterranean populations( 13 – 15 ) and a lower risk of metabolic syndrome and CVD in non-Mediterranean populations( 16 – 19 ). These findings indicate that the adoption of the MedDiet model by populations having different dietary habits is effective in reducing the risk of non-communicable disorders. The short-term – 4 weeks – consumption of a DASH diet (Dietary Approaches to Stop Hypertension), rich in fruits, vegetables, whole grains and lower amounts of SFA, improved pregnancy outcomes among GDM women( 20 ). Pre-pregnancy adherence to healthy dietary patterns( 21 ) and the MedDiet is associated with lower incidence of GDM and a better degree of glucose tolerance in no-GDM pregnant women( 22 ). In any case, the mechanisms underlying the protective effects of the MedDiet are not clear as yet. The high MUFA:SFA ratio, the increased level of PUFA, the low content of trans-fatty acids (FA) and the high content of fibres, vitamins, mineral salts and phytochemicals compounds may contribute to the beneficial effects of MedDiet( 23 – 25 ). Over the past years, researchers have focused their attention on the role of plant-derived, functional foods and their bioactive compounds in the control of various aspects of diabetes mellitus( 26 , 27 ). Among the known natural bioactive components, polyphenols have been shown to have anti-hyperglycaemic effects, antioxidant and anti-inflammatory activities and no side effects( 27 – 29 ). In addition, the increasing demand of non-fish source of n-3 PUFA is worth considering, in view of the beneficial effects of these FA in GDM women( 24 ), and during pregnancy in general, not to mention the worldwide increase in the number of vegetarians and vegans( 30 ). The knowledge of how (i.e. molecular mechanisms) and where (i.e. targets) a given biocompound acts is of crucial importance to better understand the mechanisms governing the dietary impact on the metabolic system in GDM. We found a good number of articles in English published up to August 2015 by searching in PubMed, using the key words ‘gestational diabetes mellitus’, ‘diabetes’, ‘insulin resistance’, ‘hyperglycaemia’, ‘adipokines’, ‘inflammation’, ‘microRNAs’, ‘PUFAs’, molecular mechanisms’; these key words were searched in combination with the key words ‘Mediterranean diet’, vegetables food’, ‘polyphenols’, ‘phytochemicals’, ‘bioactive compounds’. Data regarding the association between plant-derived compounds and GDM are scarce. This review discusses the current knowledge and issue about the impact of dietary polyphenols on the mechanisms and/or factors regulating glucose homoeostasis, inflammation and adipose tissue (AT) function in metabolic alterations associated with GDM. The role of n-3 FA in pregnancy is also addressed. From all these data, MedDiet bioactive compounds appear to be more and more useful players to be included in future research approaches designed to prevent and treat GDM.