• Researchers are reporting that women who follow a vegan diet in pregnancy may have a higher risk of preeclampsia and having babies with a lower birth weight.

• Experts note the sample size of vegans in the study was small and the results should be interpreted with caution.

• Dietitians say a vegan diet in pregnancy can be healthy if it is well planned.

Women who eat a vegan diet in pregnancy may have a higher risk of developing preeclampsia and having newborns with a lower birth weight.

That’s according topublished today in the journal Acta Obstetricia et Gynecologica Scandinavica that reports that newborn babies of mothers who utilized a vegan diet weighed on average 240 grams (between 8 and 9 ounces) less than babies born to mothers who followed an omnivorous diet in pregnancy.

“We observed a lower mean birth weight among the few mothers who adhered to vegan diets during pregnancy compared with omnivorous mothers. We acknowledge that finding an association in an observational study cannot lead to conclusions on causality. But future studies should put more emphasis on characterizing the diet among those adhering to vegan diets and other forms of plant-based diets during pregnancy,” the study authors wrote.

“This would allow for stronger assumptions on possible causality between any association observed with birth or pregnancy outcomes in such studies and strengthen the basis for dietary recommendations,” they added.

Details from the study on vegan diets and pregnancy

The researchers examined data from more than 66,000 pregnancies in Denmark between 1996 and 2002.

More than 98% of the mothers considered themselves omnivorous and ate both plant-based foods along with meat. About 1% were vegetarians who also ate fish and poultry while 0.3% were lacto/ovo-vegetarians and ate no meat but did eat dairy and eggs, and 0.03% were vegan.

Intake of protein was lowest among vegans and intake of macronutrients was also noticeably lower.

The authors note that their findings should be interpreted with caution, due to some of the limitations of the study.

“The number of vegan pregnancies was extremely low (.03%; 18 women) relative to the total sample size. Also, being vegan when recruited into the cohort in 1996–2002 may reflect different habits compared with those following vegan diets today,” they wrote.

“On the other hand, our findings on lower birth weight are consistent with more recent studies and the low intake of proteins and other micronutrients is in line with what has been reported in other more recent studies,” they added.

Quality of vegan diets matters

Dana Hunnes, PhD, is a senior clinical dietician at UCLA Health in California. She says the quality of a vegan diet can vary quite a bit.

“Someone can eat a vegan diet that is highly processed or one can eat a vegan diet that is whole-food driven and extremely healthy, so I would like to see far more clarification on that,” Hunnes, who was not involved in the research, told Medical News Today.

“I would venture to say that the vegan diets probably had more processed foods in them (than I’d like to see from a healthy vegan diet) and I say that due to the high fat intake and similar fiber intake as omnivorous diets. Someone following a whole-food, plant-based diet would most likely have significantly higher fiber intake,” she added.

Hunnes, who followed a vegan diet during her pregnancy, says the diet can be a healthy way of eating if done properly.

“It absolutely can be healthy, but I would recommend the help of a dietitian who can assist in planning healthy whole food vegan menu to feed mom and growing fetus properly rather than eating a lot of highly processed foods,” she said.

What is preeclampsia?

The researchers also found that there were higher rates of preeclampsia among vegan mothers than among mothers who were omnivorous.

Preeclampsia occurs when a female who previously had normal blood pressure readings suddenly has high blood pressure after 20 weeks of pregnancy.

In the United States, preeclampsia occurs in roughly.

Lauri Wright, PhD, the president of the Academy of Nutrition and Dietetics, says the preeclampsia findings of the study are surprising.

“Preeclampsia is often associated with excessive weight gain, higher intake of saturated fat, and inadequate intake of certain vitamins and minerals such as calcium and magnesium – factors that are not associated with a vegan diet,” Wright, who was not involved in the research, told Medical News Today.

“A vegan diet can be healthy during pregnancy, but it needs to be well planned,” she added. “There are some nutrients that increase during pregnancy that are harder to get with a vegan diet. These include protein, vitamin B12 and zinc. Protein needs can be met by concentrating on plant-based proteins such as lentils and beans. There are many pros to the vegan diet in pregnancy. A vegan diet is typically high in fruits, vegetables, and whole grains, which provide key vitamins, minerals, and fiber. As a result, research shows that women following a vegan diet have less gestational diabetes and neural tube defects.”

What should pregnant women eat?

does not recommend a specific diet for pregnant women.

The guidelines do recommend that pregnant women follow similar guidelines for other adults, including eating nutrient dense foods across all food groups.

A healthy eating pattern should include vegetables of all kinds, fruits, grains, at least 50% being whole grains as well as dairy, protein, and healthy oils.

Foods and beverages high in added sugar, sodium, and saturated fats should be limited.

The guidelines recommend women who are pregnant consider taking a daily prenatal vitamin supplement. This will help in meeting the required amounts of vitamin D, iron, iodine, and folic acid in pregnancy.

“The prenatal [vitamin] is especially important for pregnant women following a vegan diet because they include high levels of iron and zinc,” Wright said.

Those following a vegan diet may also need to be mindful of vitamin B12.

“B12 is another important nutrient to ensure enough of (which is in a prenatal vitamin), along with omegas (can get from algae oils and/or flax/chia/walnut), and sufficient healthy proteins (tofu, soy beans, lentils, nuts, seeds). This is where I would recommend a dietitian who can aid in meal planning for vegan diets,” Hunnes said.

Both Hunnes and Wright agree that a vegan diet can offer many health benefits across the lifespan, including pregnancy. Planning, though, is key.

“Plant-based diets consistently demonstrate health benefits, including lower prevalence of diabetes, heart disease, and cancer. The only con of plant-based diets is the more restrictive they are, the better planned they need to be in order to ensure nutrient adequacy. If someone is considering going vegan, I recommend meeting with a registered dietitian to help them achieve their health goals in a nutritional adequate manner,” Wright said.