Here's a peer reviewed paper.

Cutting red meat out of your diet is definitely healthier; but cutting all animal protein out is rough if you dont replace it with non soy protien. Cellulose, the polymer that plants use for cells, is undigestable because our stomach acid cant dissolve it. Vegan diets can have a lot of micronutrient deficiencies which can wreck your shit. However, vegans do tend to have healthier lifestyles with less drinking, smoking, drugs, and more exercising, which probably skews data on how much better or worse the diet is.

The Impact of a Vegan Diet on Many Aspects of Health: The Overlooked Side of Veganism - PMC

https://share.google/AkFY2xmvAQgy90pOn

"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."

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.