Sticking to a Mediterranean diet seems to reduce the risk of adverse outcomes across the board, although the evidence is more cohesive for pregnancy than fertility.
Sticking to a Mediterranean diet may significantly lower risks of adverse pregnancy outcomes – such as gestational diabetes and hypertension, premature birth and preeclampsia – as well as other women’s reproductive health outcomes, particularly in white populations, new systematic review and meta-analysis finds.
The Mediterranean diet is thought to affect a number of physiological mechanisms that affect female reproductive health, such as inflammation, oxidative stress and hormonal balance. But the mounting evidence has not been collated and assessed as a whole.
A recent paper, published in the American Journal of Obstetrics and Gynecology, analysed 32 studies involving over 100,000 women from childhood to adulthood to review the Mediterranean diet, which is described as high in fruit, vegetables, nuts, legumes, whole grains, healthy fats (predominantly olive oil), moderate in dairy, wine, fish, and poultry and limited in red/processed meats.
Pooling data from seven RCTs comparing Mediterranean diets to control diets, the study found that the risk of gestational diabetes and gestational hypertension, which affect over 16% and 3% of women in Australia respectively, both dropped by over a quarter in women randomised onto the Mediterranean diet. Control diets were generally participants’ usual diets, standard recommended diet or diets limiting fat.
The study also found that the risk of preterm births – almost 9% in Australian women – more than halved for those on a Mediterranean diet compared to controls, with a larger effect size if the Mediterranean diet started in the first trimester compared to after the first trimester.
“These findings suggest that the benefits of MD may differ by gestational timing, with greater benefits observed when MD interventions are initiated earlier gestation,” the researchers said.
Preeclampsia – around 3% incidence in Australia – was also reduced by 18% in those on the Mediterranean diet compared to their peers.
The protective nature of the Mediterranean diet against risk of unfavourable pregnancy outcomes was mirrored in the nine cohort studies analysed.
“Greater adherence to Mediterranean diet during pregnancy was associated with lower risks of gestational diabetes mellitus and preterm birth, consistent with findings from RCTs. Two cohort studies additionally suggested beneficial roles of prepregnancy Mediterranean diet on gestational diabetes mellitus,” the study said.
The study also analysed the effects of the Mediterranean diet on fertility.
But the data was limited to one RCT, which did not sufficiently reproduce the Mediterranean diet according to the study’s authors, and six cohort studies in women using IVF and one nested case-control study looking at fertility and the Mediterranean diet in the general population.
“Overall, no evidence of a statistically significant, beneficial association was observed from cohort studies examining successful implantation, clinical pregnancy, or live birth following IVF; however, the effect estimates were suggestive of a benefit albeit with wide CIs,” the researchers said.
“When examining the association between MD and fertility among women conceiving without medical assistance, we only identified one case-control study, which indicated that greater adherence to MD was associated with a lower risk of difficulty conceiving,” they said.
“Despite suggestive benefits on female fertility, evidence concerning a potential causal relationship among women undergoing infertility treatment or the general population is lacking,” they said.
Studies considering other female reproductive outcomes, although limited, suggested a delay in the start of menstruation and reduction in menopausal hot flashes and night sweats in those on a Mediterranean diet.
No association was found between polycystic ovary syndrome or pregnancy loss and the Mediterranean diet, although studies reviewing this were again limited.
But it wasn’t all good news: a few studies found a positive association between adherence to the Mediterranean diet and low progesterone preventing the growth of the uterine lining (luteal phase deficiency).
The effects of the diet on non-white populations remains largely unexplored, as over 95% of those assessed in this study were white.