On one hand, no diet intervention was found to significantly reduce the incidence of GDM except for the intervention of the non-randomized controlled pragmatic trial [
11] and the intervention on lifestyle (including diet) of Koivusalo et al. [
10], (see Additional file
1: Table S1). Wolff et al. [
17] found that an intensive intervention reduces the deterioration of glucose metabolism in obese pregnant women, though they did not report any incidence of GDM. Only two supplement interventions with probiotics and myo-inositol during pregnancy showed a decrease in the rates of GDM compared with a placebo. Luoto et al. [
12] intervention showed that probiotics (Lactobacillus Rhamnosus GG and Bifidobacterium Lactis Bb12) reduced the incidence of GDM; 13% (diet/probiotics) versus 36% (diet/placebo) and 34% (control),
p = 0.003. Luoto et al. [
12] explain in their article that probiotic consumption may protect against GDM because these microorganisms can modify intestinal microbiota, altering the fermentation of dietary polysaccharides and improving intestinal barrier function. They also mentioned the importance of the capability of probiotics to regulate the inflammatory pathways. It is understandable that the protection against GDM provided by probiotics, could be mediated through immunomodulatory pathways and polysaccharide fermentation. Moreover, myo-inositol supplements were found to reduce the incidence of GDM in pregnant women (Matarrelli et al. [
14]: RR = 0.127; 95% CI, 0.032–0.502;
p = 0.001 and D’Anna et al. [
13]: OR = 0.34; 95% CI, 0.17–0.68;
p = 0.001) and appear to be an insulin sensitizer. It was reported to reduce plasma glucose levels in insulin resistant conditions such as polycystic ovary syndrome and during the third trimester of GDM pregnancies [
29]. The subjacent mechanism of myo-inositol on metabolic benefits is not defined at the moment. It may produce an intracellular effect directly on the activation of acetil CoA carboxylase stimulating lipogenesis. Another theory says that it is a precursor of D-chiro-inositol, which contains inositol phosphoglycan in the extracellular matrix of the cells. It has been proposed that the binding of insulin to specific receptors stimulates D-chiro-inositol, facilitating the transport to the inside of the cell [
30]. This explains how myo-inositol interacts in the insulin-signaling cascade [
31].
On the other hand, the observational studies collected in Table S2 (Additional file
2) showed that achieving a healthier dietary pattern [
25], such a Mediterranean dietary pattern, and lowering the intake of foods with high heme iron content, sugar sweetened cola, potatoes, fatty foods and sweets, can reduce the incidence of GDM, especially among the high-risk population and before getting pregnant [
8,
21‐
23,
32‐
34].
Known evidence indicates that women who develop GDM have altered functions of β-cells and insulin resistance, limiting their capacity to cope with the metabolic challenges of pregnancy [
35]. Similarly, it is known that iron is a redox-active transitional metal, a strong pro-oxidant which promotes the creation of hydroxyl radicals, increasing oxidative stress. The pancreatic β-cell is particularly sensitive to this type of stress due to weak antioxidant protection [
36]. Nevertheless, adherence to healthy diets, such as the Mediterranean one, may reduce GDM risk by minimizing such susceptibilities before pregnancy. Common components of these dietary patterns include fruits and vegetables, relatively small amounts of red and processed meats, and high quality carbohydrates. Fruits and vegetables in particular have many antioxidant properties, in addition to providing fiber and micronutrients such as magnesium and vitamin C. The combination of all these factors may protect against metabolic deterioration counteracting free radicals and improving systemic oxidative stress [
37].