Effects of vegetarian diets on blood lipids, blood glucose, and blood pressure: a systematic review and meta-analysis

High blood lipids, blood glucose, or blood pressure ("3Bs") are established risk factors for cardiovascular diseases. However, the effects of vegetarian diets on these parameters were inconsistent in previous meta-analyses. We conducted a systematic review and meta-analysis with comprehensive subgroup analyses, quality assessment, and sensitivity analyses to confirm the effects of vegetarian diets on 3Bs. The literature was searched from PubMed, Cochrane, and Web of Science databases from the inception to February 2024. Human studies [both observational studies and randomized controlled trials (RCTs)] related to vegetarian diets and reporting 3Bs were included. The subjects were adults; the intervention/exposure was vegetarian diet which excludes the consumption of any meat, fish, and seafood and the control was an omnivorous diet; the minimum study length was two weeks. The results showed that the vegetarian diets significantly reduced the blood total cholesterol [WMD: -0.54 (95% CI: -0.60, -0.48) mmol L-1, p < 0.001 for observational studies; WMD: -0.24 (95% CI -0.37, -0.10) mmol L-1, p < 0.001 for RCTs], low-density lipoprotein cholesterol [WMD: -0.41 (95% CI: -0.48, -0.34) mmol L-1, p < 0.001 for observational studies; WMD: -0.25 (95% CI: -0.38, -0.12) mmol L-1, p < 0.001 for RCTs], and high-density lipoprotein cholesterol [WMD: -0.07 (95% CI: -0.09, -0.05) mmol L-1, p < 0.001 for observational studies; WMD: -0.07 (95% CI: -0.11, -0.04) mmol L-1, p < 0.001 for RCTs] level compared with the omnivorous diet in both healthy subjects and subjects with chronic diseases, while it had a null effect on the blood triglyceride level. In addition, the vegetarian diets significantly reduced the fasting blood glucose (FBG) [WMD: -0.35 (95% CI: -0.50, -0.21) mmol L-1, p < 0.001], glycated hemoglobin [WMD: -0.15 (95% CI: -0.28, -0.01) %, p = 0.034], and HOMA-IR [WMD: -0.98 (95% CI: -1.46, -0.51), p < 0.001] compared with the omnivorous diet, particularly when the duration was more than 12 weeks. The reduction effect on FBG was particularly significant by a vegan diet and/or in subjects with chronic diseases. The effects of the vegetarian and omnivorous diets on systolic and diastolic blood pressure were not significantly different.