what is the basis of the bolded?
I think Vitamin B12 and iron deficiency are the big ones. Along with not getting enough of the right proteins and amino acids, which is probably also an issue in the full population, but moreso with vegans/vegetarians. These things can be overcome by eating the right vegan foods, but it's complicated and a shitload of work, suggesting that most vegans are likely deficient in these areas.
Vegetarianism in any of its various forms, particularly veganism, has been increasing in popularity over the past few years, especially among the young population in the United States. While several studies have shown that a vegan diet (VD) ...
www.ncbi.nlm.nih.gov
While several studies have shown that a vegan diet (VD) decreases the risk of cardiometabolic diseases, such as cardiovascular disease, type 2 diabetes mellitus, obesity, and non-alcoholic fatty liver disease, veganism has been associated with adverse health outcomes, namely, nervous, skeletal, and immune system impairments, hematological disorders, as well as mental health problems due to the potential for micro and macronutrient deficits. The goal of this review article is to discuss the current literature on the impact and long-term consequences of veganism on vulnerable populations, including children, adolescents, pregnant and breastfeeding women, and fetal outcomes in strict vegan mothers. It also focuses on the many deficiencies of the vegan diet, especially vitamin B12, and the related increased risk of malignancies.
Protein
A recent systematic study examined the intake and adequacy of the VD in terms of macro and micronutrient intake in the adult European population. The study found that vegans consumed the least total protein compared to other diet groups, confirming concerns that VD may include insufficient protein, particularly in instances where legume, seed, and nut consumption is limited [
14]. Vegans consume fewer essential amino acids than non-vegans [
15]. Plant proteins are less digestible (50-70%) than animal proteins, and food processing methods like heating may further reduce digestibility. According to the WHO, animal proteins are considered complete proteins and have higher biological value, protein efficiency ratio, net protein utilization, and, ultimately, have a higher Protein Digestibility Corrected Amino Acid Score (PDCAAS) compared to plant proteins [
16,
17]. By and large, soy proteins constitute a significant protein source for most vegans [
18].
Vitamin B12
Low vitamin B12 intake is a significant problem in vegan diets due to the exclusion of vitamin B12-rich foods such as meat, poultry, and eggs. A lack of vitamin B12 has been linked to neurologic and hematologic problems [
19]. Low vitamin B12 intake has serious clinical consequences, although deficient symptoms appear gradually over time. High folate levels may also partly and temporarily obscure some of the typical vitamin B12 hematological manifestations. To prevent vitamin B12 deficiency, vegans must get their levels checked regularly and meet their daily requirements via supplements or fortified foods.
A growing body of research indicates that inadequate B12 consumption may contribute to carcinogenesis. Vitamin B12 deficiency increases uracil misincorporation, impairing DNA synthesis and genomic instability. Global hypomethylation of DNA is a characteristic of early carcinogenesis. Thus, if not adequately replaced, VD may inadvertently lead to cancers [
20]. Wu et al found that blood B12 levels were substantially lower in menopausal and postmenopausal breast cancer patients, and patients with the lowest B12 levels had an elevated risk of breast cancer [
21]. Reduced B12 levels have also been linked to an increased risk of cervical and gastrointestinal tract malignancies [
22-
24]. As a result, B12 supplementation is imperative for vegans due to the extensive and irreversible detrimental effects of the deficiencies.
Other minerals and micronutrients
Vegans have greater iron needs than other diet patterns [
25], mainly because non-heme iron from plant-based foods is less bioavailable, as absorption is hindered by whole grains, legumes, and nuts due to their phytic acid content [
26]. Vegans also have a zinc deficit. While meat, dairy, and eggs contain zinc, some zinc-rich plant foods (e.g., nuts, seeds, and whole grains) have poor bioavailability owing to the presence of phytate, which inhibits absorption in the gut [
16]. Inadequate zinc consumption may be associated with mental health problems (e.g., depression), dermatitis, diarrhea, and alopecia, all of which are more prevalent among vegans [
27,
28]. Selenium insufficiency has also been seen among vegetarians.
Vitamin D, calcium, bone mineral density, and risk of fractures
Numerous studies have shown that vegans consume insufficient calcium and vitamin D, not only owing to the absence of dairy products but also due to calcium bioavailability problems in plant-based diets [
28]. Vitamin D insufficiency exacerbates calcium shortage further owing to impaired intestinal absorption. After adjusting for socioeconomic variables, lifestyle covariates, and body mass index (BMI), a recent study reported that as compared to meat-eaters, there was an increased risk of hip fractures observed in vegetarians (HR 1.25; CI 1.04-1.50), vegans (2.31; 1.66-3.22), and fish eaters (1.26; 1.02-1.54) [
29]. Vegans also had a greater incidence of overall fracture (1.43; 1.20-1.70), leg fractures (2.05; 1.23-3.41), and fractures in other major sites (1.59; 1.02-2.50). The higher risk of fractures may be related to vegans' significantly lower calcium intake, reduced dietary protein intake, and lower BMI [
30-
32].
Mental health
The most recent systematic review [
33], which included eighteen studies, compared meat abstainers versus meat eaters in terms of mental health. The research included 160,257 individuals (85,843 females and 73,232 men) from various geographic areas, including 149,559 meat eaters and 8584 meat abstainers (aged 11 to 96 years). Eleven of the 18 studies found that meat-free diets were linked with worse psychological health, four were inconclusive, and three found that meat-free diets resulted in improved results. The most thorough research found that meat-avoiders (i.e., "full vegetarians") had a 7.4%, 24.1 %, and 35.2% 1-month, 12-month, and lifetime prevalence of unipolar depressive disorders, respectively. In contrast, meat consumers had a much lower prevalence: 6.3%, 11.9%, and 19.1%. Similarly, the 1-month, 12-month, and lifetime prevalence of anxiety disorders for meat abstainers were much higher at 20.4%, 31.5%, 31.5%, and 10.7%, 17.0%, and 18.4% in the meat eaters respectively. The study highlights the high incidence of mental health problems among vegans, emphasizing the vital need of increasing awareness of these illnesses to facilitate early intervention. Women notably appeared to be adversely impacted by mental disorders such as stress [
34-
36].
Orthorexia
Orthorexia nervosa (ON) is defined as a fixation on health-conscious eating behavior [
37]. It involves obsessive (compulsive) food decisions, self-imposed anxiety, self-punishment, and increasingly extreme limitations. As a result of diet-related concerns, individuals develop dietary restrictions, lack of food pleasure, inflexible and rigid eating behaviors, and ritual activities surrounding food preparations. Vegetarian, and vegan, women are more prone than males to have disordered eating attitudes and practices [
38].
Mortality
Although some studies indicate a reduction in mortality associated with vegetarianism and VD, the larger body of evidence indicates that the health benefits associated with vegetarianism may be due to other “lifestyle” factors associated with socioeconomic statuses, such as adequate physical activity, low alcohol, and drug consumption, or avoidance of tobacco products. Recently, Johnston et al. argued that the evidence supporting public health recommendations to reduce or eliminate meat intake was based on questionable studies and "inappropriate analysis" [
39]. This argument and the growing body of contrasting and conflicting findings create a conundrum for doctors and policymakers alike.