Vegan and vegetarian diets are lauded by the conventional medical and nutrition establishments for their purported health benefits. In fact, the American Dietetic Association has even stated that vegan and vegetarian diets are “appropriate during all life cycle stages, including pregnancy, lactation, infancy, childhood, and adolescence.” (1) As someone with a deep background in nutritional biochemistry and human physiology, this broad statement gives me pause – where is the evidence indicating that vegan and vegetarian diets are safe and optimal for all life stages? Given that the medical and nutrition establishments have previously been quite wrong about some important topics, such as the [lack of] relationship between saturated fat and heart disease, I hesitate to endorse their position on the safety of plant-based diets for all life stages. In this blog series, my goal is to demonstrate that vegan and vegetarian diets are not optimal for all life stages and that in some life stages, they may actually be harmful.
Studies on pregnant vegans and the “healthy user bias”
Previous research has suggested that vegan women have lower-than-average rates of cesarean delivery, less postpartum depression, lower rates of gestational diabetes and preeclampsia, and lower neonatal and maternal mortality. (2) Sounds like a good deal, right? These findings have been widely cited as evidence of the benefits and safety of vegan diets during pregnancy. However, these studies and countless other studies of vegans are confounded by a phenomenon called “the healthy user bias.” The healthy user bias is a bias that occurs in epidemiological studies when the subjects who enroll in the study are not representative of the general population, but rather, are healthier or more concerned about their health than the average person. Studies of vegans are susceptible to the healthy user bias because people who choose to become vegan often do so because they want to improve their health and believe veganism is the ticket. They are thus more likely to eat fruits and vegetables, exercise, engage in a regular stress reduction routine, and practice other health-conscious practices than the average study subject. Thus, the epidemiological studies of vegan women who had better pregnancy outcomes than the average [non-vegan] woman may merely reflect the fact that a healthier lifestyle overall, not the avoidance of animal foods, produces a healthier pregnancy.
Sex Ratio in Vegan and Vegetarian Newborns
The sex ratio is the ratio of males to females in a population. The normal sex ratio in healthy, well-nourished populations is 105/100. A low sex ratio in newborns is an indicator of the presence of environmental stressors, such as malnutrition, in mothers. A fascinating epidemiological study of 6,000 women at a British hospital found a decreased sex ratio (81.5/100 vs. 106/100) in the newborns of vegetarian vs. omnivorous mothers. (3) This finding suggests that vegetarians may be malnourished, contributing to the decreased sex ratio. As I’ll explore in the rest of this article, malnourishment is a significant possibility in pregnant vegans and vegetarians.
Nutrient deficiencies in vegan and vegetarian pregnancies
While the conventional nutrition establishment has approved the consumption of vegan and vegetarian diets during pregnancy, the potential nutrient deficiencies induced by these diets and the effects on maternal and infant health are grossly overlooked. In this section, I’d like to discuss the many nutrient deficiencies that occur in vegan and vegetarian diets and how they may adversely impact maternal and infant health both in the short- and long-term.
Omega-3 fatty acids
Omega-3 fatty acids, especially EPA and DHA, are essential for healthy fetal development. The omega-3’s EPA and DHA accumulate rapidly in the brain and retina during the later stages of pregnancy and early postnatal life, where they play a role in neurodevelopment and vision. (4) DHA and EPA are found primarily in seafood, with small amounts naturally occurring in microalgae. Vegans and vegetarians are at risk for EPA and DHA deficiencies due to their avoidance of seafood. Alpha-linolenic acid (ALA) is a precursor of EPA and DHA that is found in plant foods such as flax and chia seeds, but it is poorly converted into EPA and DHA in the body. Thus, vegan and vegetarian diets during pregnancy pose a risk of omega-3 fatty acid deficiency; this deficiency has significant implications for fetal and maternal health. Omega-3 fatty acid deficiency during pregnancy impairs fetal neurodevelopment and increases the risk of pre-term birth and postpartum depression. (4)(5) If a woman continues to remain deficient in omega-3’s during breastfeeding, the low level of DHA in her breastmilk may further impair her infant’s neurodevelopment.
Vitamin B12 is found almost exclusively in animal foods - the best sources are meat, poultry, and seafood. The only potential vegan source of B12 is a combination of nori and wild mushrooms. Claims that vitamin B12 occurs in Brewer’s yeast and certain species of algae is misleading because these plants actually contain B12 analogs called cobamides; cobamides bind to and block vitamin B12 receptors rather than activating them as true B12 does. Due to their avoidance of meat, poultry, and seafood, vegans and vegetarians are extremely susceptible to B12 deficiency. A recently published study found that a shocking 77 percent of vegetarians and 92 percent of vegans are B12-deficient compared to just 11% of omnivores! (6) Furthermore, a study of pregnant women who were long-term vegetarians found a significantly increased risk of B12 deficiency in the women. (7) B12 deficiency during pregnancy is dangerous because B12 plays critical roles in DNA and red blood cell synthesis and in neurological development; a lack of maternal B12 impairs these processes in the fetus and can cause adverse neonatal health outcomes. In fact, infants born to vegan mothers have demonstrated severe health problems associated with B12 deficiency, including hypotonia, arrest and regression of developmental skills, and megaloblastic anemia. (8) Maternal B12 deficiency also increases the risk of neural tube defects.
Can B12 supplementation correct deficiency in pregnant vegans and vegetarians? The research is mixed; several studies have found that even well-educated vegans and vegetarians do not supplement adequately with B12. Furthermore, there is some evidence to suggest that supplemental B12 may interfere with active B12, exacerbating B12 deficiency. (9) Given the alarming health implications of B12 deficiency in infants, I firmly believe that all pregnant women should consume B12-containing animal foods such as fish, poultry, or red meat. Since a vegan diet doesn’t provide these foods, pregnant women should seriously consider whether a vegan diet is something they want to toy with during pregnancy.
There are two forms of dietary iron: Non-heme iron and heme iron. Heme iron is found exclusively in animal foods such as meat, poultry, and seafood. Non-heme iron is found in plant foods, eggs, and dairy and is significantly less bioavailable than heme iron. Despite daily iron intakes similar to omnivores, vegetarians and vegans have substantially lower iron concentrations because the iron they consume, non-heme iron, is less bioavailable. (10) Iron needs increase during pregnancy, further increasing the risk of deficiency in pregnant vegans and vegetarians. Maternal iron deficiency during pregnancy decreases fetal iron stores, with adverse implications for fetal health. In fact, iron deficiency during pregnancy increases an infant’s risk of developmental difficulties, including delays in language and motor development, and impaired cognitive and social-emotional functions because iron is needed for healthy brain development. (11) Maternal iron deficiency anemia is also associated with lower birth weight infants and an increased risk of preterm delivery and perinatal complications. While vegans and vegetarians can take iron supplements, these supplements frequently cause side effect such as constipation, stomach pain, nausea, vomiting, and when taken long-term, an increased risk of iron toxicity.
Another nutrient crucial for healthy pregnancy outcomes that is often deficient in vegan and vegetarian diets is zinc. Zinc is most bioavailable when consumed in animal foods; while it is found in grains, the phytic acid in grains significantly inhibits zinc absorption. A recent review found that adult vegetarians have lower dietary zinc intakes and lower serum zinc concentrations compared to omnivores. (12) Maternal zinc deficiency during pregnancy increases the risk of fetal growth restriction and may impair neonatal vision, neurological function, and immune function. (13)(14) The most bioavailable sources of zinc are meat and shellfish.
Vegan pregnant women are at risk for calcium deficiency, which can negatively impact skeletal health. While there are a handful of plants that contain calcium, such as spinach, kale, mustard greens, almonds, and sesame seeds, these plant foods are also rich in phytic acid and oxalate, which significantly inhibit the absorption of calcium in the gastrointestinal tract. In fact, you would need to eat 16 cups of spinach to get the same amount of calcium as one glass of milk! Calcium deficiency is less of a concern for vegetarian pregnant women if they are eating dairy.
The standard American diet, vegan, and vegetarian diets all pose a risk of choline deficiency. Choline is crucial for healthy fetal and neonatal brain development. Maternal choline deficiency during pregnancy may impair brain development and increase the risk of birth defects. (15) According to Chris Masterjohn, an expert on choline, beef liver and egg yolks are hands-down the best sources of choline – they contain ten times more choline than most vegetables! To get the same amount of choline in one egg yolk, you’d need to eat 200 g of nuts or cruciferous vegetables per day. Beef liver and egg yolks are obviously not a part of vegan diets, and eggs may only be a minor part of vegetarian diets, putting pregnant vegans and vegetarians at risk for choline deficiency. Unfortunately, prenatal supplements cannot solve the problem of choline deficiency because they do not contain an adequate source of choline. Thus, choline must be obtained in the diet.
Based on the evidence I have outlined in this article, I believe vegan diets are neither safe nor optimal during pregnancy. Vegetarian diets are a safer alternative to vegan diets because they contain dairy products and eggs, which are decent sources of vitamin B12, calcium, iodine, vitamin D, and several other nutrients required for a healthy pregnancy. However, if you are genuinely looking to optimize your pregnancy and your infant's health, a whole foods-based omnivorous diet is the absolute best option because it provides all of the nutrients needed for growing a healthy human in their most bioavailable forms.