Vegetarian diet
Meta-analyses of trials, most pooling lacto-ovo and vegan diets, find vegetarian diets lower weight about 2 to 3 kg, HbA1c about 0.3 to 0.4 points in type 2 diabetes and LDL about 0.3 mmol/L. Cohorts link them to less heart disease but more stroke and hip fracture. Vitamin B12, iron and zinc status run lower.
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- Status
- A dietary pattern, not a regulated product.
- Also called
- lacto-ovo vegetarian, lacto-ovo-vegetarian, ovo-lacto vegetarian, lacto vegetarian, ovo vegetarian, meatless diet
- Followed for
- weight loss, blood sugar, type 2 diabetes, cholesterol, blood pressure, heart health, longevity
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help4
- StrongShown to lower HbA1c about 0.3 to 0.4 points against comparison diets in adults with type 2 diabetes.
- StrongShown to lower LDL cholesterol about 0.3 mmol/L against omnivorous diets in adults. HDL also fell slightly in one review.
- ModerateShown to lower weight about 2 to 3 kg against non-vegetarian diets in adults. The lacto-ovo subgroup alone did not reach significance.
- ModerateLinked to about 22 to 28% lower coronary heart disease in cohort studies, with no significant link to total cardiovascular death.
Reported risks8
- StrongLinked to vitamin B12 depletion or deficiency in 11 to 90% of vegetarians depending on age group, more in vegans and lifelong vegetarians.Very common
- StrongLinked to serum ferritin about 30 µg/L lower in adult vegetarians than non-vegetarians, with the largest gap in men.How often is not known
- StrongLinked to lower zinc intake and serum zinc in vegetarians than non-vegetarians, most in women, vegans and vegetarians in developing countries.How often is not known
- ModerateLinked to lower blood vitamin D in vegetarians than meat and fish eaters in a UK cohort, with the largest gap in winter.How often is not known
- ModerateLinked to iodine status below the WHO target range in vegetarians, second lowest after vegans, most in countries without iodized salt programs.How often is not known
- ModerateLinked to lower bone density and about 25% more hip fractures in vegetarians than meat eaters, though an earlier analysis of the same cohort found no difference.How often is not known
- LimitedLimited evidence: blood EPA and DHA were lower in vegetarian men than meat eaters and did not change with years on the diet.How often is not known
- LimitedLinked to 20% more strokes in vegetarians than meat eaters in one UK cohort, mostly hemorrhagic. A meta-analysis found no link to stroke death.How often is not known
What people follow it for, and what was found
Shown to help4
Blood sugar in type 2 diabetes
Shown to lower HbA1c about 0.3 to 0.4 points against comparison diets in adults with type 2 diabetes.
Compared with comparator diets the source does not describe [1]; control diets the source does not describe [2]
The numbers and sources
- Effect
- In 6 controlled trials (255 participants), vegetarian diets lowered HbA1c by 0.39 points (95% CI -0.62 to -0.15), and fasting glucose did not change significantly [1]. In 9 RCTs (664 participants), HbA1c fell 0.29 points (95% CI -0.45 to -0.12) and fasting glucose 0.56 mmol/L, at moderate certainty, with no change in fasting insulin [2].
- Population
- Adults with type 2 diabetes, mean age 42.5 in [1]; adults with diabetes in trials of 3 weeks or more [2].
- Sources
- [1], [2]
- Caveats
- Both reviews pooled lacto-ovo and vegan diets. Trials were small and short.
LDL cholesterol
Shown to lower LDL cholesterol about 0.3 mmol/L against omnivorous diets in adults. HDL also fell slightly in one review.
Compared with control diets the source does not describe [2]; an omnivorous control diet containing meat and dairy products [3]; an omnivorous diet [4]
The numbers and sources
- Effect
- In 11 trials, vegetarian diets lowered total cholesterol by 0.36 mmol/L, LDL by 0.34 mmol/L (95% CI -0.57 to -0.11) and HDL by 0.10 mmol/L (95% CI -0.14 to -0.06), with no triglyceride change [3]. In 30 RCTs, vegetarian or vegan diets lowered LDL by 0.30 mmol/L (95% CI -0.40 to -0.19) and apolipoprotein B by 12.92 mg/dL, with similar effects across intervention diet types and no triglyceride change [4]. In people with diabetes, LDL fell 0.12 mmol/L (95% CI -0.20 to -0.04) [2].
- Population
- Adults in randomized trials [3][4]; adults with diabetes [2].
- Sources
- [2], [3], [4]
- Caveats
- The reviews pooled lacto-ovo and vegan diets, though [4] found effects similar across diet types.
Weight
Shown to lower weight about 2 to 3 kg against non-vegetarian diets in adults. The lacto-ovo subgroup alone did not reach significance.
Compared with control diets the source does not describe [2]; non-vegetarian diets [5]; untreated control groups, which 4 of the 15 trials had [6]
The numbers and sources
- Effect
- In 12 RCTs (1,151 participants, median 18 weeks), vegetarian diets lowered weight by 2.02 kg against non-vegetarian diets (95% CI -2.80 to -1.23). The vegan subgroup lost 2.52 kg, and the lacto-ovo subgroup 1.48 kg (95% CI -3.43 to 0.47) [5]. A review of 15 trials of vegetarian diets without calorie limits, 4 of them with untreated control groups, estimated weight change against those controls at -3.4 kg by intention to treat (95% CI -4.4 to -2.4) [6]. In adults with diabetes, weight fell 2.15 kg [2].
- Population
- Adults in RCTs [5]; adults in 15 intervention trials, 4 with untreated controls [6]; adults with diabetes [2].
- Sources
- [2], [5], [6]
- Caveats
- Weight loss shrank at a year or more (-1.13 kg) [5]. Only 4 of the 15 trials in [6] had untreated controls.
Heart disease
Linked to about 22 to 28% lower coronary heart disease in cohort studies, with no significant link to total cardiovascular death.
Compared with omnivores, in cohort studies [9]; non-vegetarian dietary patterns, in cohorts [10]; meat eaters in the same UK cohort (EPIC-Oxford) [11]
The numbers and sources
- Effect
- In 10 cohorts, vegetarian diets were linked to lower incidence or death from ischemic heart disease (RR 0.75, 95% CI 0.68 to 0.82), and not to total cardiovascular disease, all-cause death or cancer death [9]. In 7 cohorts (197,737 participants), vegetarian diets were linked to lower coronary heart disease death (RR 0.78) and incidence (RR 0.72, 95% CI 0.61 to 0.85), and not to cardiovascular death (RR 0.92, 95% CI 0.84 to 1.02) [10]. In EPIC-Oxford over 18.1 years, vegetarians had 22% lower rates of ischemic heart disease than meat eaters (HR 0.78, 95% CI 0.70 to 0.87), about 10 fewer cases per 1,000 people over 10 years [11].
- Population
- Adults in prospective cohorts [9][10]; 48,188 UK adults [11]. All observational.
- Sources
- [9], [10], [11]
- Caveats
- Observational. Certainty was very low for all outcomes in [10]. The EPIC-Oxford link weakened after adjusting for cholesterol, blood pressure, diabetes and BMI (HR 0.90) [11]. Vegetarian groups in these cohorts include vegans.
Mixed results1
Blood pressure
Mixed results: one meta-analysis found systolic blood pressure about 5 mmHg lower, while trials in people with diabetes found no change.
Compared with control diets the source does not describe [2]; omnivorous diets, in 7 controlled trials and 32 observational studies [7]; omnivorous Adventists in the same cohort, white adults in the USA and Canada [8]
The numbers and sources
- Effect
- In 7 controlled trials (311 participants), vegetarian diets lowered systolic blood pressure by 4.8 mmHg (95% CI -6.6 to -3.1) and diastolic by 2.2 mmHg against omnivorous diets. In 32 observational studies, systolic was 6.9 mmHg lower [7]. In 9 RCTs in people with diabetes, blood pressure did not change [2]. In an Adventist cohort sample, lacto-ovo vegetarians had lower odds of hypertension than omnivores (OR 0.57, 95% CI 0.36 to 0.92) [8].
- Population
- Adults, mean age 44.5 in the trials [7]; adults with diabetes [2]; 500 white Adventists, observational [8].
- Sources
- [2], [7], [8]
- Caveats
- Few small trials. Heterogeneity was high in the observational studies (I² 91.4%) [7]. Part of the cohort difference reflected lower body weight [8].
How trials defined it
Vegetarian diets exclude meat, seafood and products containing them [12]. Weight trials prescribed vegetarian diets for at least 4 weeks without calorie limits [6], and RCTs ran a median 18 weeks with lacto-ovo and vegan subgroups [5]. Diabetes trials lasted 3 weeks or more [2].
Risks
Reported risks8
Vitamin B12 deficiency
Linked to vitamin B12 depletion or deficiency in 11 to 90% of vegetarians depending on age group, more in vegans and lifelong vegetarians.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- In 18 studies measuring methylmalonic acid or holotranscobalamin, deficiency rates among vegetarians were 62% in pregnant women, 25 to almost 86% in children, 21 to 41% in adolescents and 11 to 90% in older adults. Rates were higher in vegans and in people vegetarian since birth [13]. A review of 141 studies found B12 intake and status lower in vegetarians and vegans than meat eaters [14].
- Population
- Vegetarians and vegans of all ages [13]; adults in 141 studies [14]. Observational.
- Sources
- [13], [14]
- Caveats
- The B12 review combined vegetarians and vegans and drew on a PubMed search only [13].
Lower iron stores
Linked to serum ferritin about 30 µg/L lower in adult vegetarians than non-vegetarians, with the largest gap in men.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In 24 cross-sectional studies, adult vegetarians had serum ferritin 29.71 µg/L lower than non-vegetarians (95% CI -39.69 to -19.73). The gap was 61.88 µg/L in men, 17.70 µg/L in premenopausal women and 13.50 µg/L in all women [12]. A review of 141 studies found iron intake and status generally lower on plant-based diets [14].
- Population
- Adult vegetarians and non-vegetarians [12][14]. Observational.
- Sources
- [12], [14]
- Caveats
- Cross-sectional comparisons. Ferritin measures stores, and a lower value is not the same as anemia [12].
Lower zinc status
Linked to lower zinc intake and serum zinc in vegetarians than non-vegetarians, most in women, vegans and vegetarians in developing countries.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Across 26 studies, zinc intake was 0.88 mg a day lower and serum zinc 0.93 µmol/L lower in vegetarians than non-vegetarians [15]. A review of 141 studies found zinc intake and status generally lower on plant-based diets [14].
- Population
- Habitual vegetarians and non-vegetarians in 34 studies [15]; adults in 141 studies [14]. Observational.
- Sources
- [14], [15]
- Caveats
- Definitions of vegetarian varied between studies [15].
Lower vitamin D
Linked to lower blood vitamin D in vegetarians than meat and fish eaters in a UK cohort, with the largest gap in winter.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Plasma 25-hydroxyvitamin D was lower in vegetarians and vegans than in meat and fish eaters. Meat eaters averaged 77.0 nmol/L and vegans 55.8 nmol/L. The gap was larger in winter. Levels below 25 nmol/L in winter and spring ranged from under 1% to 8% across diet groups [16]. A review of 141 studies found vitamin D intake and status generally lower on plant-based diets [14].
- Population
- 2,107 white UK adults aged 20 to 76, including 420 vegetarians [16]; adults in 141 studies [14]. Observational.
- Sources
- [14], [16]
- Caveats
- Cross-sectional. The abstract does not give the vegetarian mean [16].
Low iodine status
Linked to iodine status below the WHO target range in vegetarians, second lowest after vegans, most in countries without iodized salt programs.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In 15 studies (127,094 adults), vegans had the lowest urinary iodine, followed by vegetarians, and neither reached the target status. The lowest intake recorded was in vegetarians, 15.6 µg a day [17]. In 11 studies (4,421 adults), no diet group had median urinary iodine in the WHO target range of 100 to 200 µg/L, and vegetarians and especially vegans in countries without universal salt iodization had higher risk of low status [18].
- Population
- Adults in industrialized countries [17]; adults in 11 studies [18]. Observational.
- Sources
- [17], [18]
- Caveats
- Both reviews come from the same research group. Omnivores also fell short of the target range in [18].
Lower omega-3 (EPA and DHA)
Limited evidence: blood EPA and DHA were lower in vegetarian men than meat eaters and did not change with years on the diet.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Plasma EPA and DHA proportions were lower in vegetarians and vegans than meat eaters, and did not track how long people had followed the diet [19]. A review of 141 studies found EPA and DHA intake lower in vegetarians and vegans [14].
- Population
- 196 meat-eating, 231 vegetarian and 232 vegan men in the UK [19]; adults in 141 studies [14]. Observational.
- Sources
- [14], [19]
- Caveats
- One status study, in men only. The abstract gives no sizes for the differences [19].
Lower bone density and hip fracture
Linked to lower bone density and about 25% more hip fractures in vegetarians than meat eaters, though an earlier analysis of the same cohort found no difference.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Across 20 studies (37,134 participants), vegetarians and vegans had lower bone mineral density at the femoral neck and lumbar spine than omnivores [20]. In EPIC-Oxford over 17.6 years, vegetarians had more hip fractures than meat eaters (HR 1.25, 95% CI 1.04 to 1.50), about 2.9 more per 1,000 people over 10 years [21]. An earlier EPIC-Oxford analysis over 5.2 years found no difference in total fractures for vegetarians (rate ratio 1.00, 95% CI 0.89 to 1.13) [22].
- Population
- Adults in 20 observational studies [20]; 54,898 UK adults, 15,499 vegetarians [21]; 34,696 UK adults [22].
- Sources
- [20], [21], [22]
- Caveats
- Observational. The earlier analysis used self-reported fractures [22]. The hip fracture link stayed significant after adjusting for calcium and protein intake [21].
Stroke
Linked to 20% more strokes in vegetarians than meat eaters in one UK cohort, mostly hemorrhagic. A meta-analysis found no link to stroke death.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In EPIC-Oxford, vegetarians had higher rates of total stroke than meat eaters (HR 1.20, 95% CI 1.02 to 1.40), about 3 more per 1,000 people over 10 years, mostly from hemorrhagic stroke [11]. In 7 cohorts, vegetarian diets were not linked to stroke death (RR 0.92, 95% CI 0.77 to 1.10) [10].
- Population
- 48,188 UK adults followed 18.1 years [11]; adults in 7 cohorts [10]. Observational.
- Sources
- [10], [11]
- Caveats
- Observational. The stroke link did not weaken after adjusting for disease risk factors [11]. The vegetarian group included vegans [11].
Supplements to consider
The nutrients research linked to this diet running short, each with its own page.
Vitamin B12
Strong Linked to vitamin B12 depletion or deficiency in 11 to 90% of vegetarians depending on age group, more in vegans and lifelong vegetarians.
Iron
Strong Linked to serum ferritin about 30 µg/L lower in adult vegetarians than non-vegetarians, with the largest gap in men.
Zinc
Strong Linked to lower zinc intake and serum zinc in vegetarians than non-vegetarians, most in women, vegans and vegetarians in developing countries.
Vitamin D
Moderate Linked to lower blood vitamin D in vegetarians than meat and fish eaters in a UK cohort, with the largest gap in winter.
Iodine
Moderate Linked to iodine status below the WHO target range in vegetarians, second lowest after vegans, most in countries without iodized salt programs.
Fish oil
Limited Limited evidence: blood EPA and DHA were lower in vegetarian men than meat eaters and did not change with years on the diet.
Sources
- Yokoyama Y, Barnard ND, Levin SM, et al. Vegetarian diets and glycemic control in diabetes: a systematic review and meta-analysis. Cardiovascular Diagnosis and Therapy. 2014. https://pubmed.ncbi.nlm.nih.gov/25414824/
- Viguiliouk E, Kendall CW, Kahleová H, et al. Effect of vegetarian dietary patterns on cardiometabolic risk factors in diabetes: A systematic review and meta-analysis of randomized controlled trials. Clinical Nutrition. 2019. https://doi.org/10.1016/j.clnu.2018.05.032
- Wang F, Zheng J, Yang B, et al. Effects of Vegetarian Diets on Blood Lipids: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Journal of the American Heart Association. 2015. https://doi.org/10.1161/JAHA.115.002408
- Koch CA, Kjeldsen EW, Frikke-Schmidt R. Vegetarian or vegan diets and blood lipids: a meta-analysis of randomized trials. European Heart Journal. 2023. https://doi.org/10.1093/eurheartj/ehad211
- Huang RY, Huang CC, Hu FB, et al. Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials. Journal of General Internal Medicine. 2016. https://doi.org/10.1007/s11606-015-3390-7
- Barnard ND, Levin SM, Yokoyama Y. A systematic review and meta-analysis of changes in body weight in clinical trials of vegetarian diets. Journal of the Academy of Nutrition and Dietetics. 2015. https://doi.org/10.1016/j.jand.2014.11.016
- Yokoyama Y, Nishimura K, Barnard ND, et al. Vegetarian diets and blood pressure: a meta-analysis. JAMA Internal Medicine. 2014. https://doi.org/10.1001/jamainternmed.2013.14547
- Pettersen BJ, Anousheh R, Fan J, et al. Vegetarian diets and blood pressure among white subjects: results from the Adventist Health Study-2 (AHS-2). Public Health Nutrition. 2012. https://doi.org/10.1017/S1368980011003454
- Dinu M, Abbate R, Gensini GF, et al. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Critical Reviews in Food Science and Nutrition. 2017. https://doi.org/10.1080/10408398.2016.1138447
- Glenn AJ, Viguiliouk E, Seider M, et al. Relation of Vegetarian Dietary Patterns With Major Cardiovascular Outcomes: A Systematic Review and Meta-Analysis of Prospective Cohort Studies. Frontiers in Nutrition. 2019. https://doi.org/10.3389/fnut.2019.00080
- Tong TYN, Appleby PN, Bradbury KE, et al. 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. BMJ. 2019. https://doi.org/10.1136/bmj.l4897
- Haider LM, Schwingshackl L, Hoffmann G, et al. The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis. Critical Reviews in Food Science and Nutrition. 2018. https://doi.org/10.1080/10408398.2016.1259210
- Pawlak R, Parrott SJ, Raj S, et al. How prevalent is vitamin B12 deficiency among vegetarians? Nutrition Reviews. 2013. https://doi.org/10.1111/nure.12001
- Neufingerl N, Eilander A. Nutrient Intake and Status in Adults Consuming Plant-Based Diets Compared to Meat-Eaters: A Systematic Review. Nutrients. 2021. https://doi.org/10.3390/nu14010029
- Foster M, Chu A, Petocz P, et al. Effect of vegetarian diets on zinc status: a systematic review and meta-analysis of studies in humans. Journal of the Science of Food and Agriculture. 2013. https://doi.org/10.1002/jsfa.6179
- Crowe FL, Steur M, Allen NE, et al. Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters, vegetarians and vegans: results from the EPIC-Oxford study. Public Health Nutrition. 2011. https://doi.org/10.1017/S1368980010002454
- Eveleigh ER, Coneyworth LJ, Avery A, et al. Vegans, Vegetarians, and Omnivores: How Does Dietary Choice Influence Iodine Intake? A Systematic Review. Nutrients. 2020. https://doi.org/10.3390/nu12061606
- Eveleigh ER, Coneyworth L, Welham SJM. Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets. British Journal of Nutrition. 2023. https://doi.org/10.1017/S000711452300051X
- Rosell MS, Lloyd-Wright Z, Appleby PN, et al. Long-chain n-3 polyunsaturated fatty acids in plasma in British meat-eating, vegetarian, and vegan men. The American Journal of Clinical Nutrition. 2005. https://doi.org/10.1093/ajcn/82.2.327
- Iguacel I, Miguel-Berges ML, Gómez-Bruton A, et al. Veganism, vegetarianism, bone mineral density, and fracture risk: a systematic review and meta-analysis. Nutrition Reviews. 2019. https://doi.org/10.1093/nutrit/nuy045
- Tong TYN, Appleby PN, Armstrong MEG, et al. Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC Medicine. 2020. https://doi.org/10.1186/s12916-020-01815-3
- Appleby P, Roddam A, Allen N, et al. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. European Journal of Clinical Nutrition. 2007. https://doi.org/10.1038/sj.ejcn.1602659