Prepregnancy plant-based diet may cut GDM risk

Women who follow a healthy plant-based diet before pregnancy have a lower risk of developing gestational diabetes mellitus (GDM), suggests a large, prospective cohort study presented at the ADA 2020 Annual Meeting.

“GDM is linked to adverse perinatal outcomes and increased long-term cardio-metabolic disease risk,” said presenting author Dr Frank Qian from the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, US. “[Therefore, it is] crucial to identify novel modifiable factors for the prevention of GDM.”

The study built on the known association between plant-based diets and a lower risk of type 2 diabetes (T2D) and cardiovascular disease (CVD). Based on these findings, the 2015-2020 Dietary Guidelines for Americans also recommended a healthy vegetarian diet to prevent cardio-metabolic diseases, according to Qian. 

“Due to other contributing risk factors for GDM, whether the beneficial associations of plant-based diets with T2D can be extended to GDM is not known,” he added.

For the prospective analysis, 14,926 women (aged 25–44 years) with 20,707 eligible singleton pregnancies in the Nurses’ Health Study II were assessed using a food frequency questionnaire every 4 years. Dietary intake of three categories of foods was scored as index points: healthful plant-based diet (for eg, fruits, vegetables, and whole grains), unhealthful plant-based diet (for eg, refined grains and fruit juice), and animal-based foods (for eg, eggs, dairy, and meat). [ADA 2020, abstract 189-OR]

A total of 846 incident GDM were reported among the women over 10 years of follow-up.

Based on the overall plant-based diet index (PDI), women in the highest intake quintile of plant-based diets before pregnancy had a 19 percent lower risk of GDM than the comparator group in the lowest intake quintile (adjusted relative risk [RR], 0.81, 95 percent confidence interval [CI], 0.65–1.01), with incremental risk reduction from the lowest to the highest intake quintiles (p=0.03 for trend).

Similarly, the healthful diet PDI (hPDI) showed an inverse association between healthful plant-based diet and GDM: the higher the intake, the lower the risk of GDM (RR, 0.78, 95 percent CI, 0.62–0.99 for quintile 5 vs quintile 1; p=0.04 for trend).

Although the associations were attenuated after adjusting for prepregnancy BMI, they remained significant, Qian noted.

“We estimated that prepregnancy BMI mediated 61.3 percent of the association between PDI and GDM, and 44.4 percent of the association between hPDI and GDM,” he reported.

Also, the associations persisted across subgroups regardless of age, parity, family history of diabetes, physical activity, and BMI before pregnancy.

“Our study suggests that prepregnancy adherence to plant-based diets, particularly healthful plant-based diet, may be associated with a lower risk of GDM,” Qian concluded. “These associations were substantially mediated through prepregnancy BMI.”

“Future studies are needed to address whether the associations between prepregnancy plant-based diets and GDM risk are causal,” he said.  

Qian also suggested further research to examine the role of dietary habits during pregnancy itself and whether prepregnancy plant-based diets may influence offspring health and any potential adverse effects, such as nutrient deficiencies.