It found a Mediterranean-style diet – including 30g of mixed nuts per day and extra virgin olive oil – led to a 35% lower risk of developing diabetes in pregnancy.
“Until now we did not know the effect of such a diet in high-risk pregnant women”
The diet also resulted in less weight gain, by an average of 1.25kg, during pregnancy, compared to those who received routine antenatal care.
However, the ESTEEM trial, led by Queen Mary University of London and Warwick University, found the Mediterranean diet did not cut the overall risk of adverse maternal and offspring complications.
Those behind the study said it suggested a Mediterranean diet could be an effective intervention for women who enter pregnancy with pre-existing obesity, chronic hypertension or raised lipid levels.
The authors of the trial, the results of which are published in the journal PLOS Medicine, noted that one in four mothers entered pregnancy with pre-existing obesity, hypertension or raised lipid levels.
These could then lead to pregnancy complications, including gestational diabetes and pre-eclampsia, the researchers highlighted.
“Implementing this diet seems to be effective and acceptable to women”
While a Mediterranean diet, rich in unsaturated fatty acids, had reduced incidence of cardiovascular diseases in the non-pregnant population, they said its impact had not previously been widely evaluated in pregnancy.
The ESTEEM study involved 1,252 women at five UK maternity units – four in London and one in Birmingham.
Multi-ethnic inner-city pregnant women with metabolic risk factors, including obesity and chronic hypertension, were randomised to either receive routine antenatal care or a Mediterranean-style diet in addition to their antenatal care.
The diet included a high intake of nuts, extra virgin olive oil, fruit, vegetables, non-refined grains and legumes, and moderate to high consumption of fish.
In contrast, it involved small to moderate intake of poultry and dairy products, low intake of red meat and processed meat, and avoidance of sugary drinks, fast food, and food rich in animal fat.
To promote their intake in pregnancy, participants on the Mediterranean-style diet were provided with complementary mixed nuts and extra virgin olive oil as the main source of cooking fat.
Participants also received individualised dietary advice at 18, 20 and 28 weeks’ gestation.
“We’re happy that our funding is being used to improve the health of East London mothers”
Fiona Miller Smith
The diet was made culturally sensitive by providing cooking advice through a bespoke recipe book, which incorporated elements of it into the local cuisine, developed with local community teams.
Professor Shakila Thangaratinam, from Queen Mary University of London, said: “This is the first study to show that pregnant women at high risk of complications may benefit from a Mediterranean-style diet to reduce their weight gain and risk of gestational diabetes.
“Implementing this diet seems to be effective and acceptable to women,” she said. “Current national dietary guidelines do not include the key components of the Mediterranean-style diet in their recommendations.
“Women who are at risk of gestational diabetes should be encouraged to take action early on in pregnancy, by consuming more nuts, olive oil, fruit and unrefined grains, while reducing their intake of animal fats and sugar,” she said.
Dr Bassel Wattar, from both Warwick and Queen Mary University, said: “Although a Mediterranean-style diet has been shown to reduce the risk of type 2 diabetes and cardiovascular complications in the general population, until now we did not know the effect of such a diet in high-risk pregnant women.
“Now we know that pregnant women from an inner city, high-risk, multi-ethnic population are able to adapt their diet to a Mediterranean-style, and that this can bring them important benefits including a reduction in weight gain and a lower risk of developing gestational diabetes,” he added.
The work was carried out at Barts Research Centre for Women’s Health, based at Queen Mary University of London, and funded by Barts Charity.
Fiona Miller Smith, chief executive at Barts Charity, said: “With the growing problems of diabetes and obesity in pregnant women, we’re so proud to support this study which looks at preventing these risks.”
She added: “We’re happy that our funding of the Barts Research Centre for Women’s Health is being used to improve the health of East London mothers, and in turn helping future generations.”