This study found a correlation between higher plant-to-animal protein ratios and reduced CVD (HR 0.81) and CAD (HR 0.73) risk in three large US cohorts over 30 years. No association was found with stroke. Substituting red/processed meat with plant protein, especially nuts, showed the greatest benefit. The association was stronger with higher protein density. These findings should be interpreted cautiously due to the observational design and reliance on FFQs.
This analysis of prospective cohort studies suggests a correlation between higher plant-to-animal protein ratios and reduced CVD/CAD risk, but not stroke. While the large sample size, long follow-up, and sensitivity analyses are strengths, the observational nature limits causal inference. Residual confounding and reliance on FFQs are key limitations. Substituting red/processed meat with plant protein, especially nuts, appears most beneficial. However, translating these findings into practical dietary advice requires caution. Further research, including randomized controlled trials, is needed to confirm causality and establish optimal P:A ratios for diverse populations. While the findings support existing recommendations to favor plant protein, individual dietary needs and preferences should be considered.
The abstract effectively summarizes the main findings of the study, including the inverse association between the plant-to-animal protein ratio and CVD/CAD risk, the lack of association with stroke, and the enhanced benefit with higher protein density. This concisely presents the key takeaways for readers.
This is a high-impact improvement that would enhance the clarity and precision of the abstract. The abstract should clearly state the specific plant protein sources that showed the greatest benefit when replacing animal protein. This is crucial for readers to understand the practical implications of the study and for informing dietary recommendations. Specifying the sources in the abstract, which serves as a concise overview of the entire study, ensures that this critical information is readily accessible and not buried within the main text. This enhancement would significantly improve the abstract's ability to convey the study's key findings and their practical relevance.
Implementation: Revise the abstract to explicitly mention the specific plant protein sources (nuts) that were associated with the greatest cardiovascular benefit when substituting for animal protein. For example, "Substitution analyses indicated that replacing red and processed meat with nuts showed the greatest cardiovascular benefit."
The introduction effectively establishes the context and rationale for the study by highlighting the global prevalence of CVD and the existing dietary recommendations to replace animal protein with plant protein. This clearly sets the stage for the research question and emphasizes its relevance to public health.
This is a high-impact improvement that would strengthen the introduction's articulation of the research gap and the study's specific contribution. While the introduction mentions the lack of clarity regarding the optimal plant-to-animal protein ratio, it doesn't explicitly state the unanswered questions the study aims to address. Clearly defining these questions would enhance the reader's understanding of the study's objectives and its contribution to the field. Explicitly stating the research questions would provide a more focused roadmap for the study and enhance its scientific rigor. This would also improve the reader's ability to follow the logical flow of the research and appreciate the study's contribution to addressing the knowledge gap. The introduction should be revised to include specific research questions, such as, "What is the association between the plant-to-animal protein ratio and the risk of CVD, CAD, and stroke?" and "What is the joint effect of the plant-to-animal protein ratio and protein density on CVD risk?"
Implementation: Revise the introduction to explicitly state the research questions being investigated. For example, add the following: "This study aims to address the following research questions: 1) What is the association between the plant-to-animal protein ratio and the risk of CVD, CAD, and stroke? 2) What is the joint effect of the plant-to-animal protein ratio and protein density on CVD risk? 3) How does substituting specific animal protein sources with plant protein sources affect CVD risk?"
This is a medium-impact improvement that would enhance the introduction's clarity and provide a more focused overview of the study's methodology. While the introduction briefly mentions the use of prospective cohort studies, it lacks a concise summary of the key methodological aspects, such as the specific cohorts used, the duration of follow-up, and the methods for assessing dietary intake and CVD outcomes. Including this information would provide readers with a better understanding of the study's design and allow them to quickly grasp the essential methodological details. Providing a concise methodological overview in the introduction would enhance the reader's ability to contextualize the study's findings and appreciate the strengths and limitations of the chosen approach. This would also improve the flow of the paper by bridging the gap between the rationale and the detailed methods described later. Add a brief summary of the key methodological aspects, including the cohorts (NHS, NHSII, HPFS), follow-up duration (30 years), dietary assessment (FFQs), and CVD outcome ascertainment. For example, "This study utilizes data from three large prospective cohorts (NHS, NHSII, HPFS) with a 30-year follow-up, employing food frequency questionnaires (FFQs) to assess dietary intake and validated criteria to ascertain incident CVD events."
Implementation: Add a concise summary of the key methodological aspects to the introduction. For example, include the following: "This study utilizes data from three large prospective cohorts (NHS, NHSII, HPFS) with a 30-year follow-up, employing food frequency questionnaires (FFQs) to assess dietary intake and validated criteria to ascertain incident CVD events."
The methods section clearly outlines the study design, including the use of three large, ongoing prospective cohort studies (NHS, NHSII, and HPFS). This design is a strength as it allows for the examination of long-term dietary habits and their association with CVD risk, minimizing recall bias and providing a strong foundation for causal inference.
This is a high-impact improvement that would enhance the clarity and reproducibility of the dietary assessment methods. While the section mentions the use of a validated FFQ, it lacks specific details about the FFQ versions used in each cohort and any modifications made. Given the evolution of FFQs over time, specifying the version and modifications ensures that other researchers can accurately replicate the dietary assessment and compare findings across studies. Providing these details strengthens the methodological rigor and allows for better comparison with other nutritional epidemiology studies. This would also enhance the reader's confidence in the dietary data's reliability and validity. The methods section should explicitly state the FFQ versions used in each cohort (NHS, NHSII, HPFS) and detail any modifications made to the standard questionnaires. For instance, "Dietary intake was assessed using validated semiquantitative food frequency questionnaires (FFQs) administered every 4 years (NHS: 1984, version X; NHSII: 1991, version Y; HPFS: 1986, version Z). The FFQs were modified to include [specific modifications] and exclude [specific exclusions]."
Implementation: Specify the FFQ versions used in each cohort and detail any modifications made. For example, "Dietary intake was assessed using validated semiquantitative food frequency questionnaires (FFQs) administered every 4 years (NHS: 1984, version X; NHSII: 1991, version Y; HPFS: 1986, version Z). The FFQs were modified to include [specific modifications] and exclude [specific exclusions]."
This is a medium-impact improvement that would enhance the transparency and reproducibility of the statistical analyses. While the section mentions using Cox regressions and restricted cubic splines, it lacks details about the software used and the specific procedures for handling missing data and performing the substitution analyses. Providing these details would strengthen the methodological rigor and allow other researchers to reproduce the analyses and verify the findings. This would also enhance the reader's confidence in the statistical methods and the study's conclusions. The methods section should specify the statistical software used (SAS version 9.4) and provide detailed steps for handling missing data in the analyses. It should also elaborate on the specific procedures used for the substitution analyses, including the statistical methods and software packages employed. For example, "Statistical analyses were performed using SAS version 9.4 (SAS Institute). Missing data were handled using [specific method, e.g., multiple imputation]. Substitution analyses were conducted using [specific method and software, e.g., leave-one-nutrient-out model in SAS]."
Implementation: Specify the statistical software used and provide detailed steps for handling missing data and performing the substitution analyses. For example, "Statistical analyses were performed using SAS version 9.4 (SAS Institute). Missing data were handled using [specific method, e.g., multiple imputation]. Substitution analyses were conducted using [specific method and software, e.g., leave-one-nutrient-out model in SAS]."
The results section effectively presents the key findings of the study, including the inverse association between the plant-to-animal protein ratio and CVD/CAD risk, the lack of association with stroke, and the joint effect with protein density. This clear presentation of primary outcomes directly addresses the research questions posed in the introduction.
This is a high-impact improvement that would enhance the clarity and interpretability of the results. While the section presents hazard ratios and p-values, it lacks a clear explanation of the clinical significance of these findings. Quantifying the risk reduction in terms of absolute risk or number needed to treat would provide readers with a more practical understanding of the impact of dietary changes on CVD risk. This would also enhance the translational value of the findings for clinicians and public health professionals. Providing this information would strengthen the paper by making the results more relevant to clinical practice and public health interventions. This would also facilitate the communication of the study's findings to a broader audience, including patients and policymakers. Ultimately, quantifying the clinical significance of the findings would significantly improve the study's impact by providing a more concrete understanding of the potential benefits of dietary changes.
Implementation: Calculate and report the absolute risk reduction and number needed to treat associated with a higher plant-to-animal protein ratio for CVD and CAD. This can be done using the baseline risk of CVD and CAD in the study population and the hazard ratios reported in the study. For example, "A higher plant-to-animal protein ratio was associated with an absolute risk reduction of X% for CVD and Y% for CAD over 30 years of follow-up. The number needed to treat to prevent one case of CVD/CAD over 30 years was Z."
FIGURE 1. Trends in the median plant-to-animal protein ratio in the 3 prospective cohort studies. Secular population trends of plant-to-animal protein ratio indicate changing from ~1:3 to ~1:2 across all cohorts over time. NHS, Nurses' Health Study; HPFS, Health Professionals Follow-up Study.
TABLE 1 Baseline characteristics of participants according to select deciles of the plant-to-animal protein ratio.
TABLE 2 Pooled associations of deciles of the plant-to-animal protein ratio with the cardiovascular disease outcomes.
FIGURE 2. Dose-response relationship of the plant-to-animal protein ratio with risk of cardiovascular outcomes. (A) Total cardiovascular disease, (B) coronary artery disease, and (C) stroke. Analysis was conducted after combining all 3 cohorts. Multivariable model was adjusted for age, race, smoking, menopausal status and postmenopausal hormone use, oral contraceptive use, multivitamin use, regular aspirin use, physical activity, family history of myocardial infarction, family history of diabetes, marital status, BMI, alcohol intake, total energy intake, modified AHEI score, socioeconomic status, baseline hypercholesterolemia, hypertension, and diabetes. Dose-response relationships were determined using restricted cubic splines. Solid lines represent hazard ratios and dotted lines represent 95% confidence intervals.
FIGURE 3. Joint associations of the plant-to-animal protein ratio and protein density with cardiovascular outcomes. Hazard ratios (HRs) were determined using Cox regression models. Analysis was conducted after combining all 3 cohorts. The reference group was the lower ratios and lower protein density group. Multivariable model was adjusted for the same covariates as model 3 in Table 2. No corrections for multiple tests were applied.
The discussion effectively summarizes the main findings, highlighting the inverse association between plant-to-animal protein ratio and CVD/CAD risk, the null association with stroke, and the enhanced benefit with higher protein density. This concisely reiterates the key results for the reader.
This is a high-impact improvement that would enhance the discussion's contribution to dietary recommendations. While the discussion mentions the benefits of replacing animal protein with plant protein, it doesn't provide specific, actionable dietary advice based on the findings. Translating the research into practical recommendations would increase the study's impact on public health and clinical practice. Providing clear dietary advice would empower readers to make informed choices about their protein intake and potentially reduce their CVD risk. This would also enhance the translational value of the study and bridge the gap between research and practice. The discussion should include specific dietary recommendations based on the findings. For example, "Based on our findings, we recommend that individuals aim for a plant-to-animal protein ratio of at least 0.5, prioritizing plant protein sources such as legumes, nuts, and whole grains over red and processed meat. For individuals at high risk of CAD, a higher ratio of 0.76 or greater may be beneficial."
Implementation: Add specific dietary recommendations based on the study's findings. For example, "Based on our findings, we recommend that individuals aim for a plant-to-animal protein ratio of at least 0.5, prioritizing plant protein sources such as legumes, nuts, and whole grains over red and processed meat. For individuals at high risk of CAD, a higher ratio of 0.76 or greater may be beneficial."
This is a medium-impact improvement that would enhance the discussion's scientific rigor and contribution to the field. While the discussion mentions potential mechanisms, it lacks a thorough exploration of the biological pathways linking plant-to-animal protein ratio to CVD risk. Expanding on these mechanisms would strengthen the study's scientific contribution and provide a deeper understanding of the observed associations. A more detailed discussion of the mechanisms would stimulate further research and potentially lead to the identification of new therapeutic targets for CVD prevention. This would also enhance the reader's understanding of the complex interplay between diet and CVD risk. The discussion should elaborate on the potential mechanisms linking plant-to-animal protein ratio to CVD risk. This could include discussing the role of amino acid profiles, fiber, saturated fat, and other nutrients in mediating the observed associations. For example, "The observed inverse association between plant-to-animal protein ratio and CVD risk may be mediated by several factors, including the lower saturated fat and higher fiber content of plant-based diets, as well as differences in amino acid profiles. Plant proteins are typically lower in branched-chain amino acids, which have been linked to increased CVD risk, and higher in arginine, which may have beneficial effects on blood pressure."
Implementation: Expand the discussion of potential mechanisms linking plant-to-animal protein ratio to CVD risk. Include a detailed discussion of the role of amino acid profiles, fiber, saturated fat, and other nutrients in mediating the observed associations.
FIGURE 4. Subgroup analyses for cardiovascular outcomes for 1-SD increase in the plant-to-animal protein ratio. Hazard ratios (HRs) were determined using Cox regression models. Pooled multivariable-adjusted HRs (indicated by the blue dots) and 95% CIs (indicated by black horizontal lines) of all 3 cohorts are shown. The same covariates were adjusted as model 3 in Table 2, with the exception of not adjusting for the categorical covariate when it was used as a strata. No corrections for multiple tests were applied. AHEI, Alternative Healthy Eating Index; CAD, coronary artery disease; CI, confidence interval; CVD, car-diovascular disease.
FIGURE 5. Substitution analyses for 3% energy replacement of animal for plant protein and top animal protein sources for plant protein sources and the cardiovascular outcomes. Pooled multivariable-adjusted HRs (indicated by the colored dots) and 95% CIs (indicated by the horizontal lines) of all 3 cohorts are shown. HR (95% CI) for each cardiovascular outcome associated with replacing 3% energy from animal protein with plant protein and 1 daily serving of poultry, red meat, and dairy replaced with refined grains and potatoes, whole grains, nuts, and legumes are shown. The Cox proportional hazards models included all protein foods simultaneously and models were stratified by cohort, age in moths, and follow-up period and adjusted for race, smoking, menopausal status and postmenopausal hormone use, oral contraceptive use, multivitamin use, regular aspirin use, physical activity, family history of myocardial infarction, family history of diabetes, marital status, BMI, alcohol intake, total energy intake, modified AHEI score, socioeconomic status, and baseline hypercholesterolemia, hypertension and diabetes. For the energy substitution, the leave-one-out approach to examine the isocaloric substitution of animal for plant protein and included protein density, carbohydrate density, and fat density in the models instead of the modified AHEI. For each substitution of 1 food item for another, we exponentiated the difference between the β-coefficients of the 2 foods to estimate the HR, and we used the variances and covariance of the 2 food items to estimate the 95% CI. No corrections for multiple tests were applied. Red meat included unprocessed and processed sources. AHEI, Alternative Healthy Eating Index; CI, confidence interval.