The science doesn’t agree with that

It is the position of the Academy of Nutrition and Dietetics that appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes. Plant-based diets are more environmentally sustainable than diets rich in animal products because they use fewer natural resources and are associated with much less environmental damage. Vegetarians and vegans are at reduced risk of certain health conditions, including ischemic heart disease, type 2 diabetes, hypertension, certain types of cancer, and obesity. Low intake of saturated fat and high intakes of vegetables, fruits, whole grains, legumes, soy products, nuts, and seeds (all rich in fiber and phytochemicals) are characteristics of vegetarian and vegan diets that produce lower total and low-density lipoprotein cholesterol levels and better serum glucose control. These factors contribute to reduction of chronic disease

https://pubmed.ncbi.nlm.nih.gov/27886704/

Nevertheless, several RCTs [randomized controlled trials] have examined the effect of vegetarian diets on intermediate risk factors of cardiovascular diseases (Table 1). In a meta-analysis of RCTs, Wang et al. (22) found vegetarian diets to significantly lower blood concentrations of total, LDL, HDL, and non-HDL cholesterol relative to a range of omnivorous control diets. Other meta-analyses have found vegetarian diets to lower blood pressure, enhance weight loss, and improve glycemic control to greater extent than omnivorous comparison diets (23-25). Taken together, the beneficial effects of such diets on established proximal determinants of cardiovascular diseases found in RCTs, and their inverse associations with hard cardiovascular endpoints found in prospective cohort studies provide strong support for the adoption of healthful plant-based diets for cardiovascular disease prevention

https://www.sciencedirect.com/science/article/am/pii/S1050173818300240

Well-planned vegan and other types of vegetarian diets are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence. Vegetarian diets offer a number of nutritional benefits, including lower levels of saturated fat, cholesterol, and animal protein as well as higher levels of carbohydrates, fiber, magnesium, potassium, folate, and antioxidants such as vitamins C and E and phytochemicals

https://pubmed.ncbi.nlm.nih.gov/12778049/