Cardiovascular Disease

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.

Key Points

• Aims: The study aimed to assess the association between plant-based diets and cardiovascular disease (CVD) outcomes, considering overall adherence and distinctions between healthful and less healthful plant-based diets.
  
  
• Study Design: The meta-analysis included 13 prospective cohort studies involving 410,085 participants aged 38–67 years old, BMI range of 23.0–29.7 kg/m².
  
  
• Methodology: Two authors independently reviewed articles. The study used hazard ratios and adjusted for various factors. The inclusion of recently developed plant-based indices provided a more comprehensive assessment.
  
  
• Quality assessment: Most included studies had a low risk of bias.
  
  
• Greater adherence to a plant-based dietary pattern was associated with a:
  • 8% lower risk of cardiovascular mortality (95%CI, 0.86 to 0.99, p = 0.0193, N = 124,501).
  • 10% lower risk of CVD incidence (95%CI, 0.82 to 0.98, p = 0.0173, N = 323, 854).
    
    
• Healthful plant-based diets—emphasizing whole grains, fruits, vegetables, nuts, legumes, tea, and coffee—were associated with 13% decreased CVD incidence (95%CI, 0.80 to 0.95, p = 0.0011, N = 71,301).
  
  
• Unhealthful plant-based diets (emphasizing refined grains, starches, and sugars) were associated with 5% increased CVD mortality (95%CI, 1.01 to 1.09, p = 0.0123, N = 18,966).
  
  
• Vegetarians had 19% lower CVD incidence (95%CI, 0.72 to 0.91, p = 0.004, N = 16,254). Vegetarians had a similar risk of stroke and CVD mortality compared to meat-eaters.
  
  
• Significance: Researchers utilized the PDI, allowing for a more nuanced evaluation of adherence to plant-based diets compared to previous meta-analyses. Unhealthful PDI was associated with a modest increased cardiovascular mortality, while healthful PDI was associated with a significant decrease in CVD incidence.
  
  
• Future research is needed in patients with existing CVD and in non-western populations. Additionally, future  studies should stratify by sex and examine the duration of adherence and possible dose-response relationship between intake of healthful plant foods and CVD outcomes.

Conclusion

Adherence to a plant-based diet, especially one emphasizing healthful food choices, is associated with a lower risk of cardiovascular mortality and CVD incidence. However, unhealthful plant-based diets may increase cardiovascular mortality. The study provides valuable insights into the nuanced effects of different plant-based dietary patterns on cardiovascular health.

Editor's Note: Registered dietitian nutritionists (RDNs) working with patients at risk for CVD should emphasize the favorable role of healthful plant-based foods in reducing CVD incidence and mortality.

Key Points

• Study design: Systematic review and meta-analysis of 37 publications including 24 prospective cohorts.
  
  
• Aim: This study aimed to determine the association between substituting animal-based foods with plant-based foods and cardiometabolic health outcomes, including cardiovascular diseases (CVD), type 2 diabetes (T2D), and all-cause mortality.
  
  
• Cardiovascular disease outcome:
  • Replacing processed meat with the following plant foods resulted in a significantly lower risk of CVD:
    • Nuts: 27% lower risk (95%CI, 0.59 to 0.91, n_cohorts = 8).
    • Legumes: 23% lower risk (95%CI, 0.68 to 0.87, n_cohorts = 8).
    • Whole grains: 36% lower risk (95%CI, 0.54 to 0.75, n_cohorts = 7).
  • Substituting eggs with nuts and butter with olive oil also showed a 17% (95%CI, 0.78 to 0.89, n_cohorts =8) and 4% (95%CI, 0.95 to 0.98, n_cohorts = 3) lower risk of total CVD respectively.
  • There was an indication that replacing red meat with nuts, unprocessed red meat with nuts or legumes, poultry with nuts, and eggs with legumes may also be associated with a lower risk of total CVD.
    
    
• Type 2 Diabetes (T2D) outcomes:
  • Replacing red meat with nuts, whole grains, or processed meat with nuts showed a lower risk of T2D incidence.
  • Substituting poultry with whole grains and eggs with nuts or whole grains was associated with a reduced T2D risk.
    
    
• All-Cause Mortality outcomes:
  • Replacing red meat, processed meat, dairy, poultry, eggs, and butter with plant-based options like nuts, legumes, whole grains, and olive oil was linked to a reduced risk of all-cause mortality.
    
    
• Quality of evidence: The study assessed the certainty of evidence using the GRADE approach, indicating moderate certainty for some associations, while others had low or very low certainty.
  
  
• Significance: This is the first study to summarize the relationships between substituting animal-based with plant-based foods and cardiometabolic outcomes including CVD, CHD, T2D, and all-cause mortality.

Conclusion

The findings suggest that shifting from animal-based to plant-based foods is beneficially associated with cardiometabolic health and a reduced risk of all-cause mortality. It emphasizes the potential health benefits of adopting a plant-based diet.

Editor’s Note: This study is useful for advocating simple swaps and emphasizing that better nutrition is not all-or-nothing, but that every time a whole plant-based food is chosen over an animal-based food, this is a good bet for better health. More research is needed to evaluate swapping dairy, fish, and poultry with whole plant-based foods and to evaluate swapping animal-based foods with plant-based meat and dairy replacements.

Key Points

• Aim: Evaluate the effectiveness of a vegan dietary pattern for both primary and secondary prevention of cardiovascular disease (CVD).
  
  
• Design: This systematic review and meta-analysis included 38 papers representing 13 RCTs (including 8 ongoing trials) evaluating a vegan dietary pattern in three populations: (1) healthy adults, (2) those at high risk of CVD (primary prevention), and (3) those with established CVD (secondary prevention). The vegan dietary pattern was compared either to (1) no or minimal intervention, (2) another dietary prevention aimed at preventing CVD onset, or (3) another dietary pattern for people with CVD to prevent a recurrent event.
  
  
• Outcomes: Primary outcomes included lipid levels and blood pressure. No studies reported on clinical endpoints (CVD events).
  
  
• Results: Moderate-certainty evidence that a vegan diet probably led to a small reduction in total cholesterol, LDL cholesterol, a very small decrease in HDL levels, and a very small increase in triglyceride levels compared to no or minimal intervention in people without CVD.
  • There is a lack of evidence for a significant effect on systolic and diastolic blood pressure and total cholesterol levels.
  • The studies showed little or no effect on LDL and HDL cholesterol levels or triglycerides compared to other dietary interventions.
  • There was insufficient evidence for a beneficial effect on lipid levels or blood pressure compared to other dietary interventions.
    
    
• Limitations: Studies in this review had small sample sizes and limitations in study design. Only one study was included with people who already had CVD. No study reported on CVD clinical endpoints (i.e., heart attack, heart failure, or stroke). Eight studies were ongoing so were unable to report final results.
  

Conclusion

Current evidence is insufficient to conclude the effects of vegan dietary interventions on CVD risk factors. Ongoing studies may provide more insights, particularly in the context of primary prevention.

Editor’s Note: Caution is needed in interpreting the findings due to study limitations and small sample sizes. A vegan dietary pattern is not necessarily a healthy dietary pattern and other studies have explored the different effects of healthy versus unhealthy plant-based diets. This review highlights the need for further research that includes CVD clinical endpoints, larger sample sizes, and populations with CVD. In addition, diet quality should be assessed to distinguish between healthful and unhealthful plant-based diet patterns so that accurate conclusions about the efficacy of a plant-based diet in preventing and reversing heart disease.

Key Points

• Aim: This study explored the associations between adherence to plant-based dietary patterns and the incidence of type 2 diabetes (T2D), cardiovascular disease (CVD), cancer, and mortality among adults.
  
  
• Study design: This study is a systematic review and meta-analysis of prospective observational studies that included 76 publications reporting on 55 cohorts with a total of 2,230,443 participants.
  
  
• Inverse associations were observed between higher adherence to a plant-based dietary pattern and the risks of CVD, T2D, cancer, and all-cause mortality.
  • The inverse associations were stronger when the intervention diets emphasized healthy plant-based foods like vegetables, fruits, whole grains, and legumes.
  • Inverse associations with plant-based diets and CVD were driven mainly by CHD and not stroke.
  • Vegan or vegetarian diet patterns were associated with a slightly lower risk of CVD, T2D, and cancer compared to plant-based dietary patterns (which may have included small amounts of animal foods), however, the risk reduction was similar for mortality.
    
    
• Healthy vs Unhealthy Plant-Based
  • Unhealthy plant-based diets were positively associated with these disease outcomes.
  • Healthful plant-based dietary patterns showed stronger associations with lower risk of CVD, T2D, and cancer compared to overall plant-based patterns.
    
    
• Location: The association between plant-based dietary patterns and CVD was significantly stronger in studies conducted in Asia and Australia.
  
  
• Quality of evidence: The limitations of this meta-analysis include small sample sizes in some studies, variations in study designs and analyses, differences in clinical characteristics and populations sampled, and the majority of studies lacking repeated measurement of dietary intake.
  
  
• Proposed mechanisms for the favorable effects of plant-based diets include lower energy density, potential cholesterol-lowering effects, improved blood lipid profiles, the absence or reduction of meat, and the presence of polyphenols and other beneficial nutrients.
  

Conclusion

The study suggests that plant-based dietary patterns, especially those based on healthy plant food sources, may be beneficial for the primary prevention of CVD, T2D, cancer, and mortality.

Editor’s Note: This study emphasizes the importance of diet quality and the difference between healthful and unhealthful plant-based diets. The researchers emphasize that the plant-based dietary patterns performed nearly as well as the vegan and vegetarian patterns, supporting a more flexible approach—it is easier for many people to include more healthy plant foods in their diet as opposed to eliminating all animal foods. It's important to note that these findings are based on observational studies, and further research, including randomized controlled trials, is needed to establish causation and explore the underlying mechanisms in more detail. In addition, future research is warranted to investigate the other variables responsible for the significantly greater risk reductions found in plant-based diet studies conducted in Asia and Australia.

Key Points

• Aim: The study aims to assess the relationship between plant-centered diet quality and the incidence of cardiovascular disease (CVD) over a 32-year follow-up period.
  
  
• Study design: Prospective study including 4946 adults in the CARDIA prospective study, initially aged 18 to 30, and free of CVD in 1985–1986, followed until 2018.
  
  
• Measurement: Plant-centered diet quality was assessed using the A Priori Diet Quality Score (APDQS), which emphasizes higher consumption of nutritionally rich plant foods and limited consumption of high-fat meat products and less healthy plant foods.
  
  
• Results: Both long-term consumption and a shift toward a plant-centered diet were associated with a lower risk of CVD during the 32-year follow-up.
  • Long-term consumption of a plant-centered diet was associated with a 52% lower risk for CVD (95% CI, 0.28–0.81) for the highest quintile of time-varying average APDQS compared to the lowest quintiles.
  • A shift towards a plant-based diet over 13 years was associated with a 61% lower risk of CVD (95% CI, 0.19–0.81) in the subsequent 12 years when comparing the extreme quintiles.
  • Researchers also found strong inverse associations for CHD and hypertension-related CVD.
    
    
• The study suggests that consumption of a plant-centered, high-quality diet starting in young adulthood is associated with a lower risk of CVD by middle age.
  
  
• Significance: This study provides evidence for the benefits of making long-term changes towards a more plant-based diet.
  

Conclusion

Long-term consumption of a nutritionally rich plant-centered diet is associated with a lower risk of CVD. Increased plant-centered diet quality from young adulthood is linked to a lower subsequent risk of CVD in middle age.

Editor’s Note: The findings of this study support the idea that a nutritionally rich plant-centered diet can help prevent the development of cardiovascular disease. The tool used to measure diet allowed for flexibility in food choice and scored diets based on the variety of nutrient-rich plant foods included. The authors suggest that the exclusion of all animal foods from the diet may not be necessary and that allowing small amounts of animal products while primarily focusing on nutritionally rich plant foods may help maintain long-term stability in healthy eating. The aforementioned strengths of the measurement tool, long-term follow-up design, and high retention rate, may have contributed to the significant CVD risk reduction demonstrated by this study, which is substantially greater than other studies reviewed in this brief.

Future Directions

Based on the findings from this topical review, researchers may consider the following suggestions for future research.

Diet Quality: More randomized controlled trials should be conducted to investigate the effects of plant-based diet quality on CVD risk and outcomes.

Diet Quantity: More studies are needed to determine if there is a minimally required dose of plant-based nutrition to have a clinically meaningful effect on CVD risk and outcomes.

Effects of Medication: Future studies should evaluate plant-based nutrition independent of medication use and any food/medication interactions that may affect CVD risk and outcomes.

Long-Term Adherence: Studies lasting >6 months should be conducted to investigate the effects of long-term adherence on CVD risk and outcomes.

Diverse Populations: Racial, ethnic, age, and gender differences in CVD risk and outcomes should be explored in non-western populations.

Dose-Response Relationships: Studies investigating dose-dependent relationships between types of plant-based diets (i.e., vegan, vegetarian, pescatarian etc.) and CVD risk and outcomes are needed.