--- topic: "Plant-Based Diet" title: "Vegan and Vegetarian Diets: What Research Shows" order: 1 description: "Well-planned vegetarian and vegan diets lower LDL cholesterol and heart-disease risk, but vegans need B12 and often iodine. What the research shows." question: "Are vegan and vegetarian diets healthy, and what do they miss?" answer: "Well-planned vegetarian and vegan diets are probably healthy and lower LDL cholesterol and heart-disease risk, but vegans need vitamin B12 and often iodine." actions: - "If you eat no animal foods, take a vitamin B12 supplement or use B12-fortified foods every day: B12 deficiency turned up in vegetarians of every type and age studied [1][2]." - "Favor whole plant foods (vegetables, fruit, beans, nuts, grains) over refined grains, sweets and fries (three US cohorts): healthful plant-based eating meant 25% less heart disease, unhealthful 32% more [3]." - "Ask a dietitian or doctor to check your iodine, vitamin D, calcium, zinc, iron and omega-3 (EPA and DHA); iodized salt, fortified foods or supplements may be needed [4][5]." cautions: - "Pregnancy, breastfeeding, infancy and childhood need planned diets with B12 (often iodine, DHA) from fortified foods or supplements: B12 deficiency affected 62% of pregnant vegetarians and 25–86% of children [1][2]." - "Older adults and people at risk of osteoporosis should discuss calcium, vitamin D and protein with a clinician: UK vegans had over double the hip-fracture risk of meat eaters [6]." confidence: 4 confidenceNote: "Cohorts, meta-analyses and a randomized trial agree on lower LDL cholesterol and heart-disease risk, but mortality, stroke and fracture findings are mixed and diet quality varies widely." evidenceSummary: rctCount: 1 observationalCount: 5 metaAnalysisCount: 4 totalParticipants: "340,000+ across cohorts" replicated: true newestStudyYear: 2023 references: - id: "1" pmid: "23356638" title: "How prevalent is vitamin B(12) deficiency among vegetarians?" authors: "Pawlak R, Parrott SJ, Raj S, et al." year: 2013 journal: "Nutr Rev" - id: "2" pmid: "27886704" title: "Position of the Academy of Nutrition and Dietetics: Vegetarian Diets" authors: "Melina V, Craig W, Levin S" year: 2016 journal: "J Acad Nutr Diet" - id: "3" pmid: "28728684" title: "Healthful and Unhealthful Plant-Based Diets and the Risk of Coronary Heart Disease in U.S. Adults" authors: "Satija A, Bhupathiraju SN, Spiegelman D, et al." year: 2017 journal: "J Am Coll Cardiol" - id: "4" pmid: "35010904" title: "Nutrient Intake and Status in Adults Consuming Plant-Based Diets Compared to Meat-Eaters: A Systematic Review" authors: "Neufingerl N, Eilander A" year: 2021 journal: "Nutrients" - id: "5" pmid: "36912094" title: "Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets" authors: "Eveleigh ER, Coneyworth L, Welham SJM" year: 2023 journal: "Br J Nutr" - id: "6" pmid: "33222682" title: "Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study" authors: "Tong TYN, Appleby PN, Armstrong MEG, et al." year: 2020 journal: "BMC Med" - id: "7" pmid: "26853923" title: "Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies" authors: "Dinu M, Abbate R, Gensini GF, et al." year: 2017 journal: "Crit Rev Food Sci Nutr" - id: "8" pmid: "38032644" title: "Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins: A Randomized Clinical Trial" authors: "Landry MJ, Ward CP, Cunanan KM, et al." year: 2023 journal: "JAMA Netw Open" - id: "9" pmid: "26508743" title: "Effects of Vegetarian Diets on Blood Lipids: A Systematic Review and Meta-Analysis of Randomized Controlled Trials" authors: "Wang F, Zheng J, Yang B, et al." year: 2015 journal: "J Am Heart Assoc" - id: "10" pmid: "23836264" title: "Vegetarian dietary patterns and mortality in Adventist Health Study 2" authors: "Orlich MJ, Singh PN, Sabaté J, et al." year: 2013 journal: "JAMA Intern Med" - id: "11" pmid: "31484644" title: "Risks of ischaemic heart disease and stroke in meat eaters, fish eaters, and vegetarians over 18 years of follow-up: results from the prospective EPIC-Oxford study" authors: "Tong TYN, Appleby PN, Bradbury KE, et al." year: 2019 journal: "BMJ" - id: "12" pmid: "20861171" title: "Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort" authors: "Welch AA, Shakya-Shrestha S, Lentjes MA, et al." year: 2010 journal: "Am J Clin Nutr" --- Yes, if they are well planned. In pooled cohort data, vegetarians had about 25% lower risk of ischemic heart disease than meat eaters [7], and a twin trial lowered LDL cholesterol within eight weeks [8]. The catches: vegans need a B12 supplement and often more iodine [1][5], and what you eat in place of meat matters as much as leaving it out [3]. ## How it works **Who counts.** Studies group people as meat eaters, fish eaters, lacto-ovo vegetarians (dairy and eggs), and vegans (no animal foods). "Plant-based" can also mean mostly plants with a little meat. **Cholesterol and weight.** Across 11 trials, vegetarian diets lowered total cholesterol by 0.36 mmol/L (about 14 mg/dL) and LDL cholesterol by 0.34 mmol/L (about 13 mg/dL), without changing triglycerides [9]. In 22 pairs of identical twins, eight weeks of a healthy vegan diet lowered LDL by 13.9 mg/dL more than a healthy omnivorous diet, and also lowered fasting insulin and weight [8]. **Heart disease, cancer and death.** Pooled cohorts show 25% lower ischemic heart disease and 8% lower total cancer in vegetarians, but no clear difference in overall death rates [7]. In Adventist Health Study 2, vegetarians had 12% lower all-cause mortality [10]. In the UK's EPIC-Oxford cohort, vegetarians had 22% lower ischemic heart disease but 20% higher stroke rates, mostly hemorrhagic [11]. **Quality matters.** "Plant-based" includes sweets, refined grains and fries. In three US cohorts a healthful plant-based diet went with 25% less coronary heart disease, an unhealthful one with 32% more [3]. See also the [Mediterranean diet](/mediterranean-diet/cardiovascular-and-longevity) and the [Blue Zones](/blue-zones/longevity-secrets). **What can be missing.** A review of 141 studies found plant-based eaters took in less protein (still adequate) but more fiber, folate, vitamin C, vitamin E and magnesium. Intake and status of B12, vitamin D, iron, zinc, iodine and calcium were generally lower, and so was intake of EPA and DHA. Vegans had the lowest B12, calcium and iodine intakes [4]. - *B12:* deficiency was common among vegetarians and higher in vegans [1]. See [vitamin B12](/vitamin-b12/neurological-energy-and-who-needs-it). - *Iodine:* no group, omnivores included, reached the optimal range, and vegans were lowest [5]. - *Omega-3:* non-fish-eaters' blood levels were closer to fish eaters' than their intake suggested, possibly because they convert more plant omega-3 [12]. - *Bones:* vegans had more hip fractures [6]. **Planning works.** The Academy of Nutrition and Dietetics holds that appropriately planned vegetarian and vegan diets are healthful and adequate at every stage of life, with B12 from fortified foods or supplements [2]. ## The evidence in detail ### Pooled cohorts and trials on heart health A meta-analysis of 86 cross-sectional studies and 10 prospective cohorts found lower BMI, total and LDL cholesterol and glucose in vegetarians and vegans. In the cohorts, ischemic heart disease incidence or death was 25% lower (RR 0.75, 0.68 to 0.82) and total cancer incidence 8% lower (RR 0.92, 0.87 to 0.98); total cardiovascular disease, all-cause mortality and cancer mortality did not differ significantly. Vegans had 15% lower cancer incidence (RR 0.85, 0.75 to 0.95) from a small number of studies [7]. The 11-trial lipid meta-analysis found falls in total cholesterol (-0.36 mmol/L), LDL (-0.34), HDL (-0.10) and non-HDL cholesterol (-0.30), and no change in triglycerides [9]. The Stanford twin trial (22 pairs, 44 people) gave meals for the first four weeks; the vegan twin's LDL fell 13.9 mg/dL more (95% CI -25.3 to -2.4), fasting insulin 2.9 µIU/mL more and weight 1.9 kg more. It was small, short and open-label, and one author reported funding from Beyond Meat outside the study [8]. ### Large cohorts: mortality, stroke and bones Adventist Health Study 2 followed 73,308 people for a mean 5.8 years, with 2,570 deaths. All-cause mortality was lower in all vegetarians combined (HR 0.88, 0.80 to 0.97), vegans (0.85, 0.73 to 1.01), lacto-ovo vegetarians (0.91, 0.82 to 1.00) and pesco-vegetarians (0.81, 0.69 to 0.94), but not significantly in semi-vegetarians (0.92, 0.75 to 1.13), with larger effects in men [10]. Adventists are a health-conscious group, so the results may not transfer. In EPIC-Oxford (48,188 people, 18.1 years), ischemic heart disease was 13% lower in fish eaters (HR 0.87) and 22% lower in vegetarians (HR 0.78) than in meat eaters, which for vegetarians means about 10 fewer cases per 1,000 over 10 years. The vegetarian benefit weakened to HR 0.90 (0.81 to 1.00) after adjusting for cholesterol, blood pressure, diabetes and BMI. Vegetarians had 20% more total stroke (HR 1.20, 1.02 to 1.40), about three more cases per 1,000, mostly hemorrhagic [11]. In the fracture analysis of EPIC-Oxford (about 54,900 people, 17.6 years), hip-fracture risk versus meat eaters was higher in vegans (HR 2.31, 1.66 to 3.22), vegetarians (1.25) and fish eaters (1.26); vegans also had more total fractures (HR 1.43). That is roughly 15 extra hip fractures per 1,000 vegans over 10 years, and it persisted after adjusting for calcium and protein [6]. ### Plant-food quality In the Nurses' Health Study, Nurses' Health Study II and Health Professionals Follow-up Study (about 209,000 people, 8,631 coronary events), an overall plant-based index was weakly protective (HR 0.92, 0.83 to 1.01, top versus bottom decile). A healthful index (whole grains, fruit, vegetables, nuts, legumes, oils, tea and coffee) gave HR 0.75 (0.68 to 0.83), while an unhealthful one (juices, sweetened drinks, refined grains, potatoes, sweets) gave HR 1.32 (1.20 to 1.46) [3]. ### Nutrient gaps A systematic review of 141 studies (its authors work for Unilever, which sells fortified foods) found nutrient inadequacies across all diet patterns, including meat-based ones [4]. A review of 18 articles using functional B12 markers reported deficiency in 62% of pregnant women, 25% to 86% of children, 21% to 41% of adolescents and 11% to 90% of older adults among vegetarians, with higher rates in vegans and in people vegetarian from birth [1]. A meta-analysis of 11 studies (4,421 adults) found no group within the optimal urinary iodine range of 100 to 200 µg/L, with vegans lowest, particularly where salt is not iodized [5]. In EPIC-Norfolk (14,422 people with diet diaries; 4,902 with plasma fatty acids), non-fish-eaters took in 57% to 80% as much omega-3 as fish eaters, yet blood differences were far smaller [12]. ### Where the evidence conflicts All-cause mortality is lower in Adventists but not significantly different in the pooled analysis. Stroke and fracture signals come mainly from one UK cohort. Vegetarians in these cohorts are often more health-conscious, so confounding is likely, and diets were self-reported. We found no long-term trial of hard outcomes; the twin trial lasted eight weeks. ### Bottom line Confidence is 4 of 5. Well-planned vegetarian and vegan diets reliably lower LDL cholesterol and are associated with less heart disease. They carry real nutrient risks, above all B12 and iodine, and possible bone and stroke risks that need more study.