If pregnant or breastfeeding on a vegan diet, take vitamin B12 supplements or consume fortified foods; infant complementary foods must include animal-source foods, and consult a pediatrician before imposing a strict vegan diet

Vitamin B12 occurs naturally almost exclusively in animal-source foods (meat, poultry, eggs, fish, and dairy). If an expectant or nursing mother eats a strict vegan diet without supplementation, her breast milk becomes profoundly deficient in B12. Breastfed infants typically manifest clinical consequences between 4 and 8 months of age: growth failure, severe developmental delay, hypotonia, and microcephaly, with prolonged deficiency causing irreversible neurological damage. Complementary infant feeding must incorporate animal-source foods daily.

A bottle of vitamin B12 supplements costs only a few dollars for several months' supply (one tablet daily). Adding eggs, meat, or fish to infant complementary foods costs minimal additional money. The primary friction is overcoming cognitive inertia or family dietary beliefs if the household assumes a pure vegan diet is unconditionally healthier for infants.

A Centers for Disease Control and Prevention (CDC) investigation documented severe neurologic impairment in exclusively breastfed infants of vegan mothers due to cobalamin (vitamin B12) deficiency. In one clinical case, an infant whose mother had adhered to a strict vegan diet for 7 years was hospitalized at 15 months old presenting with profound failure to thrive, severe megaloblastic anemia, and brain MRI showing severe global cerebral atrophy. Despite immediate high-dose intramuscular cyanocobalamin therapy producing hematologic recovery, cognitive and expressive speech delays persisted at 32 months of age. The CDC emphasized that maternal dietary deficiency is the leading cause of infantile cobalamin deficiency, typically emerging between 4 and 8 months of age. Because natural plant-derived B12 analogues are biologically inactive or poorly absorbed in humans, unfortified plant foods cannot provide reliable cobalamin. CDC guidance mandates that all vegan and vegetarian women who are pregnant or nursing obtain adequate daily B12 via reliable fortified foods or supplements. Similarly, the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) 2017 Committee on Nutrition position paper states that all infants require nutrient-dense, iron-rich complementary foods including meat or fortified foods, warning that vegan diets should be undertaken only under rigorous medical or dietetic supervision with parents explicitly warned of potential catastrophic developmental outcomes. Public health guidelines reinforce that daily complementary feeding must include at least four food groups, encompassing at least one animal-source food, one vegetable, and one staple grain or tuber.

Controversy: The Academy of Nutrition and Dietetics (AND, 2016) states that well-planned vegetarian and vegan diets can be nutritionally adequate for all life stages, including pregnancy, lactation, infancy, and childhood. However, AND explicitly emphasizes that vegans must consume reliable sources of vitamin B12 through regular fortified foods or dietary supplements. While professional societies debate whether pure vegan feeding of infants is advisable even with supplementation, there is absolute scientific consensus across all medical bodies that maternal vegan diets require mandatory B12 supplementation. Lacto-ovo vegetarians face lower risk, but individuals consuming minimal dairy or eggs remain susceptible to subclinical depletion. Early infant B12 deficiency symptoms are non-specific (lethargy, feeding difficulties, hypotonia); CDC notes standard newborn blood counts may not detect early neurologic deficiency before structural injury occurs. If an infant displays growth stalling or motor regression, parents must proactively inform clinicians of the family's dietary pattern. Do not reject evidence-based therapies in favor of unverified alternative diets (see Chapter 16, Rule 4). Introducing complementary solids at 6 months is covered in Chapter 20, Rule 4; prenatal folic acid supplementation is covered in Chapter 27, Rule 1. Benefit magnitude is categorized as Moderate based on prevention of irreversible neurological disability. Primary beneficiaries are infants and nursing mothers.

Centers for Disease Control and Prevention (2003). Neurologic impairment in children associated with maternal dietary deficiency of cobalamin—Georgia, 2001. MMWR, 52(4), 61-64. https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5204a1.htm；Fewtrell M, Bronsky J, Campoy C, et al. (2017). Complementary Feeding: A Position Paper by the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) Committee on Nutrition. Journal of Pediatric Gastroenterology and Nutrition, 64(1), 119-132. https://doi.org/10.1097/MPG.0000000000001454；国家卫生健康委办公厅 (2020). 婴幼儿喂养健康教育核心信息. https://www.gov.cn/zhengce/zhengceku/2020-08/01/content_5531915.htm；Melina V, Craig W, Levin S (2016). Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. Journal of the Academy of Nutrition and Dietetics, 116(12), 1970-1980. https://doi.org/10.1016/j.jand.2016.09.025（备注里的反方，收益栏里的 B12 来源也出自这里）