Women who adhere to vegan diets in pregnancy have a higher risk of having a baby with a lower birth weight than omnivorous moms; and may also be at increased risk of developing preeclampsia, March of Dimes funded researchers in Denmark found in a study earlier this year.
Pregnant women who avoided all animal products, from meat, chicken, and fish; to eggs and dairy, delivered babies weighing an average of 240 grams less than babies born to moms who ate both plant and animal products, the study found. That figure constitutes about a week of fetal weight gain in the third trimester. (The average baby weighs around 3,320 grams at 40 weeks).
The study also found that vegan women were at a significantly higher risk of developing preeclampsia compared to their omnivorous counterparts 11.1% vs. 2.6%.
Published in international women’s health journal Acta Obstetricia et Gynecologica Scandinavica, the work was led by Dr. Signe Hedegaard, an obstetrician and scientist at Copenhagen University’s Juliane Marie Center, a hospital specializing in women’s reproductive health, childbirth, and pediatrics.
Dr. Hedegaard said that while the study still needed to be validated in larger, more diverse populations before a casual link could be made, the results pointed to a credible association between maternal protein intake and baby birth weight.
“Low protein intake might be a plausible explanation for lower birth weight among vegan mothers,” she said, adding that Danish health recommendations state pregnant women should get 10-20% of daily calories from protein. “With mean protein intake [among vegan mothers] being only 10.4% of energy in our study, around half of our vegan participants were below current recommendations. In the study, we concluded that further research is needed regarding possible causality between plant‐based diets and pregnancy and birth outcomes to strengthen the basis for dietary recommendations.”
A vital macronutrient, protein is composed of amino acids, which serve as both sources of energy and chemical elements like carbon and nitrogen that are essential for fetal metabolism, development, and growth during all stages of pregnancy.
While plant products also contain protein, it's rare, though not impossible, to find a plant protein that contains all nine essential amino acids crucial for the human body. Even if a vegan mom-to-be meets protein requirements with plant-based sources, Dr. Hedegaard said, some of the micronutrients that come with animal products that play an important role in healthy fetal growth may be missed.
“Some plant-based proteins, like quinoa, do contain all nine essential amino acids,” Dr. Hedegaard said. “[But] meat proteins are highly bioavailable and come with a package of other critical nutrients such as heme iron, which is better absorbed than non-heme iron found in plants, vitamin B12, and DHA. While plant-based diets can meet protein needs, they often require careful planning to avoid deficiencies in iron, B12, DHA, and other micronutrients. Inadequate intake of these nutrients can potentially lead to complications.”
The connection between veganism and preeclampsia identified in the study was less clear.
Dr. Hedegaard said the biological pathway between low protein intake and preeclampsia was still a mystery, and stressed that the large increase in risk for vegan moms—quadruple the risk of omnivore—should be taken with a grain of salt due to the small number of vegan women included in the study. Of the 66,738 Danish women involved, only 18 identified as vegan. Due to the small vegan sample size, the preeclampsia risk skewed high; and may be an overestimation of risk for this population. Other studies have indicated that a vegan or vegetarian diet during pregnancy might reduce the risk of hypertension or preeclampsia.
Still, Dr. Hedegaard said, it is a link her team will continue to probe in further studies.