IMPORTANCE: Plant-based diets are known to improve cardiometabolic risk in the general population, but their effects on people at high risk of cardiovascular diseases (CVDs) remain inconclusive.
OBJECTIVE: To assess the association of vegetarian diets with major cardiometabolic risk factors, including low-density lipoprotein cholesterol (LDL-C), hemoglobin A1c (HbA1c), systolic blood pressure (SBP), and body weight in people with or at high risk of CVDs.
DATA SOURCES: This meta-analysis was registered before the study was conducted. Systematic searches performed included Embase, MEDLINE, CINAHL, and CENTRAL from inception until July 31, 2021.
STUDY SELECTION: Eligible randomized clinical trials (RCTs) that delivered vegetarian diets in adults with or at high risk of CVDs and measured LDL-C, HbA1c or SBP were included. Of the 7871 records screened, 29 (0.4%; 20 studies) met inclusion criteria.
DATA EXTRACTION AND SYNTHESIS: Two reviewers independently extracted data including demographics, study design, sample size, and diet description, and performed risk of bias assessment. A random-effects model was used to assess mean changes in LDL-C, HbA1c, SBP, and body weight. The overall certainty of evidence was evaluated using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool.
MAIN OUTCOMES AND MEASURES: Mean differences between groups in changes (preintervention vs postintervention) of LDL-C, HbA1c, and SBP; secondary outcomes were changes in body weight and energy intake.
RESULTS: Twenty RCTs involving 1878 participants (range of mean age, 28-64 years) were included, and mean duration of intervention was 25.4 weeks (range, 2 to 24 months). Four studies targeted people with CVDs, 7 focused on diabetes, and 9 included people with at least 2 CVD risk factors. Overall, relative to all comparison diets, meta-analyses showed that consuming vegetarian diets for an average of 6 months was associated with decreased LDL-C, HbA1c, and body weight by 6.6 mg/dL (95% CI, -10.1 to -3.1), 0.24% (95% CI, -0.40 to -0.07), and 3.4 kg (95% CI, -4.9 to -2.0), respectively, but the association with SBP was not significant (-0.1 mm Hg; 95% CI, -2.8 to 2.6). The GRADE assessment showed a moderate level of evidence for LDL-C and HbA1c reduction.
CONCLUSIONS AND RELEVANCE: In this study, consuming a vegetarian diet was associated with significant improvements in LDL-C, HbA1c and body weight beyond standard therapy in individuals at high risk of CVDs. Additional high-quality trials are warranted to further elucidate the effects of healthy plant-based diets in people with CVDs.
| Discipline Area | Score |
|---|---|
| Family Medicine (FM)/General Practice (GP) |  |
| General Internal Medicine-Primary Care(US) | |
| Public Health |  |
| Endocrine | |
| Internal Medicine | |
| Cardiology | |
This meta-analysis included studies that followed participants for only 6 months on a vegetarian diet. Longer-term studies are needed.
As a family physician, this well conducted systematic review shows results I would expect. It's relevant to highlight 2 limitations: many of the studies emphasized a low-fat diet and vegetarians in the US consistently consume healthier food groups. Also, most of the studies had a high risk of bias. Perhaps the changes in LDL and HbA1c could be because of eating healthier and low-fat foods besides a plant-based diet.
This study yields valuable insights into a vegetarian diet and cardiovascular factor with firm conclusions that are limited because of the small sample sizes of the included studies precluding subgroup analysis to explain variations within a vegetarian diet and also the short-term follow-up.
The reduction of HbA1c and LDL-c due to vegetarian diet is well known. No data here are about the cardiovascular outcomes of interest such as myocardial infarction, heart failure, cardiovascular death, and stroke. These endpoints may be more useful in clinical practice.
