Dinu, M, Abbate, R, et al. Vegetarian, Vegan Diets and Multiple Health Outcomes: A Systematic Review with Meta-Analysis of Observational Studies. Crit Rev Food Sci Nutr 57(17)3640-9.
This comprehensive meta-analysis showed a significant reduced risk for the development and mortality of ischemic heart disease and cancer amongs people following a vegetarian diet.
Tantamango-Bartley, Y, Knutsen, SF, et al. Are Strict Vegetarians Protected against Prostate Cancer? Am J Clin Nutr 103(1)153-60. PMC4691666
Vegan diets showed a statistically significant protective association with prostate cancer risk. This protection is even better in black males compared to white males.
McCarty, M. Vegan Proteins May Reduce Risk of Cancer, Obesity, and Cardiovascular Disease by Promoting Increased Glucagon Activity. Med Hypotheses. Aug;. 53(6)459-85.
This is a speculation that a higher intake of non-essential amino acids without an unnecessarily high intake of essential amino acids protect against modern western diseases. Vegans tend to have low blood lipids, less body fat, shorter stature, later puberty, and decreased risk for certain prominent 'Western' cancers; a vegan diet has documented clinical efficacy in rheumatoid arthritis. Low-fat vegan diets may be especially protective in regard to cancers linked to insulin resistance such as breast and colon cancer.
McCarty, M. Upregulation of Lymphocyte Apoptosis as a Strategy for Preventing and Treating Autoimmune Disorders: A Role for Whole-Food Vegan Diets, Fish Oil and Dopamine Agonists. Med Hypotheses. Aug;. 57(2)258-75. PMID: 11461185
Based on theoretical speculation of some of the biochemical pathways and what is evident in some communities this study concluded that a whole-food vegan diet, coupled with fish oil and vitamin D supplementation will protect against autoimmune diseases.
McCarty, M, Barroso-Aranda, J, et al. The Low-Methionine Content of Vegan Diets May Make Methionine Restriction Feasible as a Life Extension Strategy. Med Hypotheses. 72(2)125-8.
This study tweezes out the positive effects which a low-methionine (an amino acid) diet, such as a plant based diet, has on longevity. It explains the phenomenon as a decrease in Insulin Growth Factor, a known aging factor. This is amplified by exercise training and the consumption of ample amounts of fruit, wine and beer! Plant protein sources are lower in methionine compared to animal derived proteins. The authors assumed a supplementation in vitamin B12 which is not as abundant in plants.