The prospective cohort study followed 11,459 women older than 18 years and evaluated their diet from the beginning using a validated questionnaire about the frequency and quality of plant-based foods. The participants had taken part in the Nurses’ Health Study II (1991-2009). From responses on the questionnaire, the investigators calculated the plant-based diet index (PDI) even among participants with an omnivorous diet. A higher score indicated greater adherence to the PDI.
“We wanted to know how one’s diet leading up to pregnancy influences the pregnancy, so we monitored women for virtually their entire reproductive life – almost 20 years – and gained an awareness of their typical diet before pregnancy,” study author Jorge E. Chavarro, MD, ScD, told this news organization. Dr. Chavarro is a professor of nutrition, epidemiology, and medicine at Harvard Medical School, Boston, and Harvard University’s School of Public Health in Cambridge, Mass. He researches how nutrition and lifestyle influence reproductive health and overall lifelong health in women.
Analysis of the data from the Nurses’ Health Study II revealed that as the proportion of animal products in diets decreased and the proportion of plant-based products increased, the risk of women experiencing hypertensive disorders of pregnancy decreased as well. Women in the highest PDI quintile had a significantly lower risk of hypertensive disorders of pregnancy, in comparison with those in the lowest quintile (relative risk, 0.76). This association was slightly stronger for pregnancy-related hypertension (RR, 0.77) than for preeclampsia (RR, 0.80).
Women in the highest PDI quintile had a 24% lower risk of hypertensive disorders of pregnancy than those in the lowest quintile; the risk of pregnancy-related hypertension decreased in a linear fashion as PDI increased, while the relationship of PDI to preeclampsia was restricted to women in the quintile with the highest adherence.
“It was clearer for pregnancy-related hypertension than for preeclampsia, but a diet made up primarily of plant-based foods seemed to be protective for both,” said Dr. Chavarro. He added that in addition to the problems these conditions cause during pregnancy, both increase the risk of subsequently developing other chronic diseases. “Could it be that modifiable lifestyle factors before and during pregnancy may not only help reduce problems during gestation but also prevent women’s health problems years later? That was the general motivation for this study.”
Mercedes Sotos-Prieto, PhD, a researcher at the Autonomous University of Madrid and an associate professor at Harvard University’s School of Public Health, told this news organization that the study’s methodology was very robust and that the investigators utilized appropriate statistical techniques for the analysis. She highlighted the fact that they used a validated food frequency questionnaire. She believes the study is also important because of the population group it focused on. “There has always been greater resistance when it comes to the diet of pregnant women, and the same is true for older adults. But we have seen that this type of diet, if it’s a quality diet, may be associated with health benefits.” She did not participate in the study.
Dr. Sotos-Prieto has a doctorate in nutritional epidemiology and public health. She works with large epidemiologic cohorts, such as the cohort of American nurses on which this study was based, and ENRICA, a cohort that is representative of the Spanish population and the population of older adults. She is the author of other studies that, like this one, found an association between a plant-based diet and a lower risk of frailty, both in the study involving American nurses and in a study involving a cohort of individuals aged 60 years or older in Spain (ENRICA-1).
Dr. Sotos-Prieto is also principal investigator on a project assessing the risk of cardiovascular disease based on modifiable lifestyles. For this project, the researchers created a tool, the healthy heart test, that can be used to evaluate diet quality “in 5 minutes, because we all know that doctors don’t have any time.” She thinks this test could be implemented in clinical practice to identify lifestyle behaviors that can be improved, such as by replacing refined cereals with whole grains or increasing legume consumption.