A study in Spain found that early intervention with a Mediterranean diet supplemented with additional extra virgin olive oil (EVOO) and pistachios reduces the incidence of gestational diabetes mellitus (GDM) and improves outcomes for mother and baby.

According to the American Diabetes Association, GDM is an important public health problem, creating complications in seven percent of all pregnancies. The prevalence of GDM is increasing as obesity, sedentary lifestyle, and older age at pregnancy become more common.

Previous studies have revealed that adherence to the Mediterranean diet decreases the risk of GDM, but this is the first randomized, controlled study of how a supplemented Mediterranean diet influences rates of GDM, as well as premature birth, emergency cesarean section, and perineal trauma.

For this study, conducted by the San Carlos Clinical Hospital in Madrid, 2,418 women were invited to participate when they came for their first pregnancy ultrasound, between eight and twelve weeks. Out of that number, 1,000 met the initial study criteria of being 18 years of age or older, having no intolerance to nuts or EVOO, and experiencing their first pregnancy. Any medical conditions or drug therapy that might compromise the effectiveness of the test diet were also ruled out. Of 1,000, 874 stayed with the study and participated all the way through the birth of their babies.

Participants were randomly assigned to either the intervention group (IG) or the control group (CG). Both groups were given the same basic Mediterranean guidelines, which included two or more daily servings of vegetables, three or more servings of fruit (excepting fruit juices), three daily servings of skimmed dairy products and whole grain cereals, two to three weekly servings of legumes, and moderate to high consumption of fish.

They were also asked to consume low amounts of red and processed meats, and avoid refined grains, processed baked goods, pre-sliced bread, soft drinks, fresh juices, fast foods and pre-cooked meals. In addition, it was recommended that they walk at least 30 minutes a day.

In addition to the basic recommendations, the 434 participants in the intervention group received guidance from dietitians a week before the study start. They were advised to consume at least 40 mL of EVOO and a handful (25-30 grams) of pistachios daily. To ensure that they had access to the minimum amount of recommended oil and nuts, each IG participant received 10 liters of EOO and two kilograms of roasted pistachios.

By contrast, the 440 control group participants were advised by their midwives to restrict consumptions of dietary fat, including nuts and EVOO.

For the length of their pregnancies, both the IG and CG had the same standard-practice laboratory evaluations, at 24-28 week’s gestation, at 36-38 weeks (third trimester), and at delivery. For both groups, nutritional guidance was reinforced at each visit. Up until delivery, all were screened for gestational diabetes, gestational weight gain, and pregnancy-induced hypertension. Individual dietary recommendations were given in cases where the patient might be consuming too many calories.

With the same frequency of guidance, testing and health-provider intervention, the gestational and birth experiences of the intervention and control groups were significantly different.

Of the 974 study participants, 177 were diagnosed with gestational diabetes. Those with GDM in the control group numbered 103, while those in the intervention group—the group whose diet included additional EVOO and pistachios—numbered 74. In addition, those in the IG with gestational diabetes had significantly reduced rates of insulin-treated GDM. And fewer of those diagnosed with GDM in the IG required insulin than those diagnosed with GDM in the CG.

In addition to experiencing fewer incidences of GDM, the intervention group bore fewer babies with low birth weight. According to the Children’s Hospital of Philadelphia, “Low birthweight is a term used to describe babies who are born weighing less than 2,500 grams (5 pounds, 8 ounces).

In contrast, the average newborn weighs about 8 pounds.” In the control group, 17 babies were assessed to have low birth weight, compared to only five babies with low birth weight in the intervention group. In addition, twenty-five of the control group babies were considered small for their gestational age, compared with five in the intervention group.

In addition, at the time of birth, fewer mothers in the IG group experienced pregnancy-induced hypertension, perineal trauma, and urinary tract infections. And, while nutritional counseling was provided to both groups, participant gestational weight gain was significantly lower at 24–28 weeks and at 36–38 weeks for participants in the intervention group.

There have been previous studies of nutritional intervention in gestational diabetes using a variety of dietary guidelines, including alternate Mediterranean (aMED), Dietary Approaches to Stop Hypertension (DASH), and alternate Healthy Eating Index (aHEI) dietary patterns.

The interventions used in these were different than the present study. Some studies based their recommendations on the restriction of saturated fats and consumption of carbohydrates with a low-glycemic index. While other studies provided recommendations like this one, this is the first study to measure the results of specifically increasing EVOO and nuts in the diets of pregnant women, as well as providing free supplies to participants.

According to the results of this study, increased EVOO and pistachio consumption were clearly beneficial. As a rich source of monounsaturated fatty acids, EVOO is known to lower glucose levels after eating and reduce inflammation.

Researchers also hypothesize that in this study’s population, the liberal use of olive oil may have facilitated an increased intake of vegetables, which are traditionally eaten with olive oil in Spanish cuisine.



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