Table 1.
Health impact of vegetarian diets in comparison to omnivorous diets: summary of meta-analyses of cohort studies and randomised controlled trials.
| Study | Title | Year | Outcomes | Studies | N | Effect (vegetarian vs omnivorous)a,b |
|---|---|---|---|---|---|---|
| Dinu et al. | Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies | 2016 | Multiple health outcomes | n =10 cohort studies | 72,298 | IHD incidence and/or mortality: RR = 0.75 (95% CI, 0.68–0.82); Incidence total cancer: vegetarians RR = 0.92 (95% CI,0.87–0.98) vegans RR = 0.85 (95% CI, 0.75–0.95); All-cause mortality: vegetarians RR = 0.94ns (95% CI, 0.86–1.04) vegans RR = 0.88ns (95% CI, 0.75-1.02); Total cardiovascular disease incidence/mortality: RR = 0.93ns (95% CI, 0.86–1.00); Cerebrovascular disease incidence/mortality: RR = 0.93ns (95% CI, 0.78–1.10); Breast cancer incidence: RR 0.94ns (95% CI, 0.84–1.06); Colorectal mortality: RR = 0.90ns (95% CI, 0.76–1.05); Breast cancer mortality: RR = 0.94ns (95% CI, 0.56–1.58); Prostate cancer mortality: RR = 0.90ns (95% CI, 0.63–1.29); Lung cancer mortality: RR = 0.86ns (95% CI, 0.62–1.19) |
| Godos et al. | Vegetarianism and breast, colorectal and prostate cancer risk: an overview and meta-analysis of cohort studies | 2016 | Prostate cancer, breast cancer, colo-rectal cancer | n = 6 cohort studies | 686,629 | Breast cancer: RR = 0.96ns (95% CI, 0.88–1.05); Colorectal cancer: RR = 0.88ns (95% CI, 0.74–1.05); Prostate cancer: RR = 0.83ns (95% CI, 0.63–1.10) |
| Huang et al. | Cardiovascular Disease Mortality and Cancer Incidence in Vegetarians: A Meta-Analysis and Systematic Review |
2012 | Cardiovascular Disease Mortality and Cancer Incidence | n = 7 cohort studies | 124,706 | IHD mortality: RR = 0.71; (95% CI, 0.56–0.87) Cancer incidence: RR = 0.82; (95% CI, 0.67–0.97) |
| Iguacel et al. | Veganism, vegetarianism, bone mineral density, and fracture risk: a systematic review and meta-analysis | 2019 | Bone Health | n = 19 cohort studies | 37 134 | Lumbar spine BMD MD: 0.032; (95% CI, - 0.048 to - 0.015); subgroup vegans MD, - 0.070; (95% CI, - 0.116 to - 0.025), vegetarians MD: 0.023; (95% CI, 0.035 to 0.010) Femoral neck BMD MD: 0.037; (95% CI, - 0.054 to −0.020), subgroup: vegetarians MD: 0.025; (95% CI, - 0.038 to - 0.012), vegans MD, - 0.055; (95% CI, - 0.090 to - 0.021); Whole body BMD MD: 0.048; (95% CI, - 0.080 to - 0.016); subgroup vegans MD: 0.059; (95% CI, 0.106 to 0.012): vegetarians MD: 0.035ns; (95% CI, 0.093 to 0.023); Fracture risk RR: 1.316; (95% CI, 1.038–1.668); Subgroup vegans RR 1.439; (95% CI, 1.047–1.977); vegetarians RR: 1.254ns; (95% CI, 0.917–1.714) |
| Kwok et al. | Vegetarian diet, Seventh Day Adventists and risk of cardiovascular mortality: A systematic review and meta-analysis | 2014 | Risk cardiovascular mortality | n = 8 cohort studies | 183,321 | Adventists vs non-Adventists mortality risk: RR = 0.68 (95% CI, 0.45–1.02) vs RR = 1.04 ns (95% CI, 0.98–1.10) IHD: RR = 0.60 (95% CI, 0.43–0.80) vs RR = 0.84 (95% CI, 0.74–0.96) Cerebrovascular disease: RR = 0.71 (95% CI, 0.41–1.20) vs RR = 1.05 ns (95% CI, 0.89–1.24) |
| Lee et al. | Adherence to a Vegetarian Diet and Diabetes Risk: A Systematic Review and Meta-Analysis of Observational Studies | 2017 | Diabetes risk | n = 14; 2 cohort 12 cross sectional | not reported | Cohorts: OR = 0.64 (95% CI, 0.57–0.74); Cohorts and Cross-Sectional: vegetarians OR = 0.73 (95% CI, 0.61–0.87); vegans OR = 0.59 (95% CI, 0.39–0.91) |
| Barnard et al. | A Systematic Review and Meta-Analysis ofChanges in Body Weight in Clinical Trials of Vegetarian Diets | 2015 | Weight reduction | n = 4 RCTs | 453 | Intention-to-treat analysis MD: 3.4 kg (95% CI, -4.4 to -2.4) Completer analysis MD: 4.6 kg (95% CI, -5.4 to -3.8) |
| Huang et al. | Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials | 2015 | Weight reduction | n = 12 RCTs | 1151 | MD: −2.02 kg (95% CI, -2.80 to -1.23) |
| Viguiliouk et al. | Effect of vegetarian dietary patterns on cardiometabolic risk factors in diabetes: A systematic review and meta-analysis of randomized controlled trials | 2018 | Cardiometabolic risk factors in diabetes | n = 9 RCTs | 664 | HbA1c (n = 8) MD: 0.29% (95% CI, -0.45 to -0.12) Glucose MD (n = 6): -0.56 mmol/L (95% CI, -0.99 to −0.13) LDL-C MD (n = 6): -0.12 mmol/L (95% CI, -0.20 to −0.04) Non-HDL-C MD (n = 7): -0.13 mmol/L (95% CI,-0.26 to - 0.01) HDL-C (n = 8): 0.03 mmol/L ns (95% CI, 0.08, 0.02) Body weight MD (n = 6): 2.15 kg (95% CI, -2.95 to-1.34 kg) Triglycerides MD (n = 7): 0.14 mmol/Lns (95% CI, -0.10 to 0.38) SBP MD (n = 7): 0.10 mmHgns (95% CI, -2.33 to 2.52) DBP MD (n = 7): 0.53 mmHgns (95% CI,-0.50 to 1.57) |
| Wang et al. | Effects of Vegetarian Diets on Blood Lipids: A Systematic Review and Meta-Analysis of Randomized Controlled Trials | 2015 | Blood lipids | n = 11 RCTs | 832 | Total cholesterol MD: -0.36 mmol/L (95% CI, -0.55 to - 0.17) LDL-C MD: -0.34 mmol/L (95% CI, -0.57 to - 0.11) HDL-C MD: -0.10 mmol/L (95% CI, -0.14 to -0.06) Non–HDL-C MD: -0.30 mmol/L (95% CI, -0.50 to -0.10) Triglycerides MD: 0.04 mmol/Lns (95% CI, -0.05 to 0.13) |
| Yokoyama et al. | Association between plant-based diets and plasma lipids: a systematic review and meta-analysis | 2017 | Blood lipids | n = 19 RCTs | 1484 | Total cholesterol MD: -12.5 mg/dL (95% CI, - 17,8 to −7,2) LDL-C MD: -12.2 mg/dL (95% CI, -17,7 to -6,7) HDL-C MD: -3.4 mg/dL (95% CI, -4,3 to -2,5) Triglycerides MD: 5.8ns mg/dL (95% CI, -0.9 to 12,6) |
| Yokoyama et al. | Vegetarian diets and glycaemic control in diabetes: a systematic review and meta-analysis | 2014 | Glycaemic control in diabetes | n = 6 RCTs | 255 | HbA1c MD: -0.3% (95% CI, --0.62 to -0.15) Glucose MD: -0.36 mmol/L (95% CI, -1.04 to -0.32) |
| Yokoyama et al. | Vegetarian Diets and Blood Pressure A Meta-analysis |
2014 | Blood pressure | n = 7 RCTs | 311 | SBP MD: -4.8 mm Hg (95% CI, -6.6 to -3.1) DBP MD: -2.2 mm Hg (95% CI: -3.5 to -1.0) |
N, number of pooled individuals; MD, mean difference; CI, confidence interval; RR, relative risk; OR, odds ratio; IHD, ischemic heart disease; BMD, bone mineral density; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; SBP, systolic blood pressure; DBP, diastolic blood pressure.
a
All effect differences are between total vegetarian and omnivorous populations except when described.
b
All effects are significantly difference except when described; ns non-significant.