Findings published in Acta Obstetricia et Gynecologica Scandinavica point to a higher prevalence of preeclampsia in vegan mother, with their newborns weighing an average of 240 g less, compared with omnivorous mothers.
“Further research is needed regarding possible causality between plant-based diets and pregnancy and birth outcomes, to strengthen the basis for dietary recommendations,” said the authors.
Commenting on plausible explanations for lower birth weight among vegan mothers, the Danish research team identified low protein intake as one possible cause, adding: “[…S]tudies have suggested a link between low protein intake, calcium or vitamin D and preeclampsia.
“[However,] the overall evidence for such a relationship is at best inconsistent and our findings would need replication before stronger conclusions can be drawn.”
Low intake of vitamins and minerals could also play role in lower birth weight
Keith Godfrey, professor of epidemiology and human development at the University of Southampton, said it was equally possible that any effect could result from low intake of vitamins and minerals.
“[These would be] primarily obtained from meat and dairy products but not necessarily present in many supplements,” he said. “Nonetheless, the study points to a need for further research.”
The findings come at a time when interest in strict adherence to plant-based diets such as veganism has been surging in many Western societies, fuelled by environmental, ethical, and animal welfare concerns.
The Retail Times estimates that 2.5 million UK adults were following a vegan diet at the start of 2024, which equates to 4.7% of the population.
This figure has grown by an impressive 1.1 million since last year when the annual research from personal finance comparison site finder.com found that there were an estimated 1.4 million vegans in the UK (2.5%).
Veganuary: A growing movement across Europe and the US
Meanwhile, YouGov surveys in 2023 found that 4% of UK respondents had participated in Veganuary for at least part of the month, rising to 7% in the US and 9% in Germany.
For the study, 65,872 women identified themselves as omnivorous, with 666 as fish/poultry vegetarians, 183 as lacto/ovo vegetarians, and 18 as vegans.
Based on a questionnaire completed mid-pregnancy, investigators found that protein intake was lower among lacto/ovo vegetarians (13.3%) and vegans (10.4%) compared with omnivorous participants (15.4%).
Micronutrient intake was also much lower among vegans, but when dietary supplements were considered, no major differences were observed.
“Our findings on higher prevalence of preeclampsia among vegan than omnivorous mothers require careful interpretation given the number of vegan participants in our study and the fact that two previous studies, with a larger sample size of vegans, have not found any indication of hypertensive disorders during pregnancy among vegans,” wrote the study authors, who are based at the universities of Copenhagen and Southern Denmark.
Small vegan number in study makes it hard to fully interpret data
Dr Duane Mellor, registered dietitian and senior lecturer at Aston Medical School, at Aston University, agreed with this observation, adding: “Although the overall number of women included in this study was large at over 65,000, the studies only included 18 people who identified as being vegan.
“The very small number of vegans who took part means that there is a risk of statistical error and that could explain the higher rates of pre-eclampsia reported in vegans.
“As there were only two women who presented with pre-eclampsia who were vegan, it could be due to variability and chance.
“This study aimed to consider protein as a mediating factor, which due to the small number of women who were vegan in the study makes it very hard to fully interpret any meaning from this data.”
