Gestational Diabetes Cut With Plant-Based Diet Before Pregnancy

Becky McCall

June 18, 2020

Healthy plant-based diets prior to pregnancy may help lower the risk of gestational diabetes, data from a large, prospective cohort study indicate.

"From these results, we can say that a pre-pregnancy plant-based diet, particularly one that also limits unhealthful plant-based foods such as refined grains, potatoes, and sugar-sweetened foods and beverages, may be associated with a lower risk of gestational diabetes," Frank Qian, MD, from the Harvard T.H. Chan School of Public Health, Boston, Massachusetts, told Medscape Medical News.

Qian and colleagues found a 19% reduction in risk for gestational diabetes in those who had followed a richer overall plant-based diet prior to pregnancy after adjusting for age, parity, race, family history of diabetes, smoking, physical activity, alcohol, total energy, margarine intake, and body mass index (BMI).

Qian presented the findings during the virtual American Diabetes Association (ADA) 80th Scientific Sessions.

He added that "another benefit of plant-based diets is reduced consumption of certain animal-based foods, particularly red and processed meats, which seem particularly adverse in terms of increasing gestational diabetes risk."

The study aimed to build on existing knowledge that plant-based diets are associated with a lower risk of type 2 diabetes and cardiovascular disease (CVD), and to see if this held true for gestational diabetes.

Jacinda Nicklas, MD, from the University of Colorado, Boulder, who also presented work during the same session, recognized the importance of this area of research but acknowledged the difficulty in finding ways to prevent gestational diabetes.

"This study may spark some interest in testing the impact of a healthy plant-based diet for high risk women, given...we know plant-based diets improve health in general," she said, adding that it showed an important association but not a causal link. 

"We don't know if plant-based diets actually decrease the risk. It could be that women who tend to eat healthy plant-based diets also tend to be healthier in other ways," she observed.

Identifying Modifiable Risk Factors to Prevent Gestational Diabetes

Gestational diabetes occurs in 7.6% of all pregnancies in the United States and is linked to adverse perinatal outcomes as well as increased long-term cardiometabolic risk. It is also associated with long-term obesity and other metabolic disorders in the child.

"It is crucial to identify novel modifiable risk factors that we can act on to prevent gestational diabetes," said Qian.

Dietary guidelines for Americans (2015-2020) recommend a healthy vegetarian diet as one means of lowering risk for type 2 diabetes and CVD.

"The vitamins, nutrients, and polyphenols found in plant-based foods...might help weight maintenance, improve glycemic control, improve blood pressure and inflammation, and so forth, and therefore reduce risk of type 2 diabetes and CVD," Qian observed.  

But it remains unknown whether the beneficial effects of plant-based diets would extend to gestational diabetes.

Qian stressed diets in the study were not vegetarian or vegan per se, as "even participants who were most adherent to a plant-based diet still consumed several servings of animal foods per day."

For the study, data were drawn from the ongoing prospective Nurses' Health Study II, comprised of nearly 117,000 women aged 25-44 years.

They completed a biennial questionnaire on lifestyle habits and disease outcomes. Dietary information was collected by food frequency questionnaires every 4 years.

Dietary intake was categorized and scored according to three classifications: healthful plant-based index diet (for example, whole grains, fruits, vegetables); unhealthful plant-based (for example, fruit juice and refined grains), and animal-based foods (such as dairy, eggs, and meat).

Points were given or taken away depending on consumption of the different food types to give an overall score on the plant-based diet index (PDI).

Participants were then divided into five quintiles according to their PDI intake, which showed a 17-point difference between quintile five, the healthiest intake, and quintile one (mean PDI score was 63 in quintile five vs 46 in quintile one). 

Recorded physical activity ranged from around 20 to 29 metabolic equivalent hours/week, and caloric intake from approximately 1500 to 2100 calories/day between quintiles one and five; other factors were roughly similar.

The main outcome was first-time incidence of gestational diabetes.

Healthy Plant Diet Cut Diabetes, but Unhealthy One Didn't Increase It 

A total of 846 new cases of gestational diabetes were documented among 20,707 eligible singleton pregnancies from nearly 15,000 women between 1991 and 2001.

The analysis showed a strong inverse association between plant-based diet and gestational diabetes with a 30% reduced risk in the highest quintile versus the lowest (risk ratio, 0.70; P = .0004), after adjustment for age, parity, race, family history of diabetes, smoking, physical activity, alcohol, total energy, and margarine intake.

"After adjustment for pre-pregnancy BMI, this was attenuated to 0.81 (P = .03)," Qian reported, suggesting the association was substantially mediated via the BMI before pregnancy, he stressed.

The researchers also identified a 13% lower risk of gestational diabetes for every 10-point increment on the plant-based diet index for individuals with higher adherence to the plant-based diet.

Of interest, however, no significant associations were observed for the unhealthy plant-based diet index.

"There was no increase in risk as we had hypothesized," Qian observed.

He added that it was an observational study and the researchers would like to investigate causality.

And they did not collect data on diet during pregnancy, so it would be important to examine the influence of this on gestational diabetes.

"Also, it's important to look at how these plant-based diets may influence offspring health as well as adverse effects, for example lack of certain nutrients, in the mother and offspring. Animal-based diets may offer specific nutrients not found in plant-based diets," Qian said.

Adding further comment, Nicklas noted that body weight and physical activity were controlled for, but she pointed out that because the Nurses Health Study II only sends surveys every 2 years, the authors might not have had up-to-date information about weight and physical activity in the period immediately preceding or during pregnancy.

"Similarly, the food frequency questionnaires are sent every 4 years, and so diet just before or during pregnancy may not be captured, and there may be other unmeasured factors that are contributing to the decreased rate of gestational diabetes but would not be included in the analysis."

ADA 2020 Scientific Sessions. Presented June 15, 2020. Abstract 189-OR.

Qian and Nicklas have reported no relevant financial relationships.

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