Vegetarian Nutrition (VN) DPG Public Library

Wang T , Kroeger C, Cassidy S, et al.
Journal: JAMA Network Open
Published: 2023

Key Points

• Plant-based diets are known to improve cardiovascular disease risk factors, but evidence about their application in people with cardiovascular disease is less clear.

• Aims: The authors aimed to evaluate the effectiveness of a vegetarian diet on 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 for, cardiovascular disease.

• Study Design: This study is a systematic review and meta-analysis of 20 randomized controlled trials that included 1,878 participants. Mean duration of intervention was 25.4 weeks (range, 2–24 months). Studies targeted people with CVDs, diabetes, and those with at least 2 CVD risk factors.

• Methodology: Two independent researchers extracted data from these studies, evaluated them for bias risk, and graded the evidence using a standardized tool.

• Quality of evidence: Overall risk of bias was moderate to high in most studies. The level of evidence was rated moderate for LDL-C and HbA1c reduction and low for SBP and weight reduction.

• Associations with Vegetarian Diets: Consuming vegetarian diets for an average of 6 months was associated with:

  • Decreased LDL-C by 6.6mg/dL (95%CI, −10.1 to −3.1)

  • Decreased HbA1c by 0.24% (95%CI, −0.40 to −0.07)

  • Decreased body weight by 3.4 kg (95%CI, −4.9 to −2.0)

• No significant association with SBP (−0.1mmHg; 95%CI, −2.8 to 2.6).

• Population Stratification:

  • The greatest reduction in LDL-C was observed in individuals at high risk of CVD.

  • Vegetarian diets were most effective in glycemic control among people with type 2 diabetes.

  • Favorable changes in weight were observed in people at high risk of CVD and those with type 2 diabetes.

• Subgroup Analyses: Lacto-ovo vegetarian diets were associated with the greatest reduction in LDL-C. Vegan diets led to a reduction in HbA1c.

• A greater reduction in body weight was observed in interventions without energy restriction.

• Medication Usage: Most participants were taking medication for suboptimal cardiometabolic profiles. Some studies reported a reduction in medication dose for hyperglycemia, dyslipidemia, and/or hypertension. The use of medication may obscure the potential effect of a plant-based diet. This is supported by two studies that prohibited medication use and found significant lowering effects of a plant-based diet on LDL-C and SBP.

• Diet Quality and Adherence:

  • 1/3 of the studies did not emphasize the consumption of plant-based whole foods, which may have influenced effect size since unhealthy plant-based diets are associated with increased cardiometabolic risk factors.

  • Limited dietary data hindered a thorough evaluation of diet quality and adherence.

  • Different forms of vegetarian diets may have varying impacts on cardiometabolic outcomes.

• Significance: First meta-analysis that analyzed RCTs evaluating the effect of vegetarian diet in in people with CVD.

• Limitations: Only four studies included populations with CVD. Most studies did not restrict medication use and 1/3 did not emphasize diet quality. Additionally, most studies were in Western countries, which could limit the generalizability of results. Most studies were of relatively short duration.

• Future research is needed that assesses plant-based diet quality, quantity, and cooking methods in people with CVD, evaluates diet independent of medication, and examines longer term adherence (past 6 months) and outcomes.

Conclusion

Consuming a vegetarian diet is associated with a modest but significant effect in reducing key cardiometabolic risk factors, especially in high-risk patients.

Editor’s Note: It's important to note that while the findings suggest positive associations, the overall quality of evidence varies, and individual dietary choices within the broader category of "vegetarian" diets may influence outcomes differently. Limitations of the studies in this review, including confounding variables such as medication usage and diet quality, should be considered when interpreting the results.