Association between plant-based diets and plasma lipids: a systematic review and meta-analysis

Abstract

Context: Although a recent meta-analysis of randomized controlled trials showed that adoption of a vegetarian diet reduces plasma lipids, the association between vegetarian diets and long-term effects on plasma lipids has not been subjected to meta-analysis.

Objective: The aim was to conduct a systematic review and meta-analysis of observational studies and clinical trials that have examined associations between plant-based diets and plasma lipids.

Data sources: MEDLINE, Web of Science, and the Cochrane Central Register of Controlled Trials were searched for articles published in English until June 2015.

Study selection: The literature was searched for controlled trials and observational studies that investigated the effects of at least 4 weeks of a vegetarian diet on plasma lipids.

Data extraction: Two reviewers independently extracted the study methodology and sample size, the baseline characteristics of the study population, and the concentrations and variance measures of plasma lipids. Mean differences in concentrations of plasma lipids between vegetarian and comparison diet groups were calculated. Data were pooled using a random-effects model.

Results: Of the 8385 studies identified, 30 observational studies and 19 clinical trials met the inclusion criteria (N = 1484; mean age, 48.6 years). Consumption of vegetarian diets was associated with lower mean concentrations of total cholesterol (-29.2 and -12.5 mg/dL, P < 0.001), low-density lipoprotein cholesterol (-22.9 and -12.2 mg/dL, P < 0.001), and high-density lipoprotein cholesterol (-3.6 and -3.4 mg/dL, P < 0.001), compared with consumption of omnivorous diets in observational studies and clinical trials, respectively. Triglyceride differences were -6.5 (P = 0.092) in observational studies and 5.8 mg/dL (P = 0.090) in intervention trials.

Conclusions: Plant-based diets are associated with decreased total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol, but not with decreased triglycerides.

Systematic review registration: PROSPERO number CRD42015023783. Available at: https://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42015023783.

Keywords: high-density lipoprotein cholesterol; low-density lipoprotein cholesterol; meta-analysis; plant-based diets; plasma lipids; systematic review; total cholesterol.

Figure 1

Flow diagram of the literature search process. Abbreviations: LDL-C, low-density lipoprotein cholesterol; Obs, observational study.

Figure 2

Pooled plasma lipid responses to vegetarian diets in observational studies. Effects on (A) TC (total cholesterol), (B) LDL-C (low-density lipoprotein cholesterol),

Figure 2

(C) HDL-C (high-density lipoprotein cholesterol), and (D) triglycerides are depicted as squares; error bars indicate 95%CIs. Meta-analysis yielded pooled estimates of TC (−29.2 mg/dL; 95%CI, −34.6, −23.8; P < 0.001); LDL (−22.9 mg/dL; 95%CI, −27.9, −17.9; P < 0.001); HDL-C (−3.6 mg/dL; 95%CI, −4.7, −2.5; P < 0.001); and triglycerides (−6.5 mg/dL; 95%CI, −14.0, 1.1; P = 0.092), which are depicted as black diamonds. Vegan diets were defined as those that omitted all animal products; vegetarian diets may include some animal products, as indicated by the terms lacto (dairy products), ovo (eggs), and pesco (fish). Reference numbers of studies are shown in parentheses.

Figure 3

Pooled plasma lipid responses to vegetarian diets in clinical trials. Effects on (A) TC (total cholesterol), (B) LDL-C (low-density lipoprotein cholesterol),

Figure 3

(C) HDL-C (high-density lipoprotein cholesterol), and (D) triglycerides are depicted as squares; error bars indicate 95%CIs. Meta-analysis yielded pooled estimates of TC (−12.5 mg/dL; 95%CI, −17.8, −7.2; P < 0.001); LDL-C (−12.2 mg/dL; 95%CI, −17.7, −6.7; P < 0.001); HDL-C (−3.4 mg/dL; 95%CI, −4.3, −2.5; P < 0.001); and triglycerides (5.8 mg/dL; 95%CI, −0.9, 12.6; P = 0.090), which are depicted as black diamonds. Vegan diets were defined as those that omitted all animal products; vegetarian diets may include some animal products, as indicated by the terms lacto (dairy products) and ovo (eggs). Reference numbers of studies are shown in parentheses.