Abstract
Background and aims: The relationships between dietary protein intake and risk of all-cause, cardiovascular disease (CVD), and cancer mortality are still unclear. We conducted a systematic review with meta-analysis of cohort studies to summarize the evidence. Methods and results: We searched PubMed and Web of Science for relevant studies through February 2020. The associations of total, animal, and plant proteins with all-cause, CVD, and cancer mortality were evaluated. Study-specific relative risks (RR) were pooled using the fixed effect model when no significant heterogeneity was detected; otherwise the random effect model was employed. Twelve cohort studies were eligible for the study. Increased total protein showed no clear association with risk of all-cause, CVD, and cancer mortality. In the stratified analysis by protein sources, higher plant protein intake was associated with a reduced risk of all-cause mortality (highest vs lowest intake: RR = 0.92; 95% CI: 0.88, 0.96; each 3% increment of intake: RR = 0.97; 95% CI: 0.94, 0.99), and may be associated with a reduced risk of CVD mortality (highest vs lowest intake: RR = 0.90; 95% CI: 0.80, 1.01; each 3% increment of intake: RR = 0.95; 95% CI: 0.91, 0.99). Moreover, higher intake of animal protein may be associated with an increased risk of CVD mortality (highest vs lowest intake: RR = 1.11; 95% CI: 1.01, 1.22; each 3% increment of intake: RR = 1.02; 95% CI: 0.98, 1.06). Conclusion: This study demonstrates that higher plant protein intake is associated with a reduced risk of all-cause and CVD-related mortality. Persons should be encouraged to increase their plant protein intake to potentially decrease their risk of death.
Generated Summary
This study presents a systematic review and meta-analysis of cohort studies investigating the associations between dietary protein intake and the risk of all-cause, cardiovascular disease (CVD), and cancer mortality. The research aimed to synthesize existing evidence from published studies to clarify the relationships between different sources of protein (total, animal, and plant) and mortality risks. The methodology involved a comprehensive search of PubMed and Web of Science databases up to February 2020, identifying relevant cohort studies. The study evaluated the associations of total, animal, and plant proteins with all-cause, CVD, and cancer mortality. Study-specific relative risks (RR) were pooled using the fixed-effect model when heterogeneity was not significant; otherwise, a random-effects model was employed. The study included 12 cohort studies. The researchers analyzed the data to determine if there were correlations between protein consumption and mortality risks.
Key Findings & Statistics
- The study included a total of 12 cohort studies.
- The included studies were conducted in North America (n = 4), Europe (n = 4), Asia (n = 3), and multi-countries (n = 1).
- The 12 studies had a total of 483,615 men and women, with 68,876 deaths.
- Eight studies reported on the total, animal, and plant protein analyses.
- The pooled RR for the highest intake compared to the lowest intake for total protein was 0.97 (95% CI: 0.89, 1.07), with moderate heterogeneity (I² = 68.9%, P = 0.001).
- The pooled RR was 0.99 (95% CI: 0.96, 1.01) per 3% increment of energy from total protein intake.
- Higher plant protein intake was associated with a lower risk of all-cause mortality (highest vs lowest intake: RR = 0.92; 95% CI: 0.88, 0.96; I² = 35.6%, P = 0.156).
- The pooled RRs were 0.97 (95% CI: 0.94, 0.99) and 1.00 (95% CI: 0.98, 1.04) per 3% increment of energy from plant and animal protein intakes, respectively.
- Animal protein was not associated with risk of all-cause mortality (highest vs lowest intake: RR = 1.04; 95% CI: 0.95, 1.14; I² = 68.9%, P = 0.004).
- The pooled RR for the highest intake compared with the lowest intake was 1.01 (95% CI: 0.93, 1.10).
- Higher intake of plant protein may be associated with a lower risk of CVD mortality (highest vs lowest intake: RR = 0.90; 95% CI: 0.80, 1.01; I² = 51.7%, P = 0.053).
- Higher intake of animal protein was associated with an increased risk of CVD mortality (highest vs lowest intake: RR = 1.11; 95% CI: 1.01, 1.22; I² = 51.0%, P = 0.069).
- Total, animal, and plant proteins were not associated with risk of cancer mortality.
- The pooled RRs for the highest intake compared with the lowest intake for total, animal, and plant proteins were 0.96 (95% CI: 0.89, 1.04; I² = 41.1%, P = 0.117), 1.00 (95% CI: 0.93, 1.07; I² = 38.1%, P = 0.152) and 0.96 (95% CI: 0.88, 1.04; I² = 0%, P = 0.752), respectively.
- The pooled RRs were 0.98 (95% CI: 0.95, 1.00), 0.98 (95% CI: 0.92, 1.03) and 1.00 (95% CI: 0.97, 1.02) for per 3% increment of energy from total, plant and animal protein intakes, respectively.
Other Important Findings
- Increased total protein showed no clear association with risk of all-cause, CVD, and cancer mortality.
- Higher plant protein intake was associated with a reduced risk of all-cause mortality.
- Higher animal protein intake may be associated with an increased risk of CVD mortality.
- Higher plant protein intake may be associated with a reduced risk of CVD mortality.
- No indication of publication bias was detected for any of the analyses.
- The study found that higher plant protein intake was associated with reduced risk of all-cause and CVD-related mortality.
- The dose-response analysis showed that for every 3% increment of energy from plant protein intake, there was a 3% and 5% lower risk of all-cause and CVD-related mortality, respectively.
Limitations Noted in the Document
- The study did not search non-English databases, which could lead to publication bias.
- Due to the observational design, residual confounding may have distorted the observed associations.
- Misclassification of protein intake, due to the self-reported nature of exposure, may have occurred.
- Significant heterogeneity was observed among study results.
- The range of protein intake between the high and low categories varied between studies.
- The size of the cohort and the length of follow-up also varied.
Conclusion
The findings from this meta-analysis suggest that the source of dietary protein may be an important factor in determining mortality risks. The results indicate that higher plant protein intake is associated with a reduced risk of both all-cause mortality and CVD-related mortality. Conversely, higher intake of animal protein may be linked to an increased risk of CVD mortality. These results align with previous research indicating that plant-based diets are beneficial for cardiovascular health and overall longevity. The study did not find a significant association between total protein intake and mortality risk, indicating that the specific source of protein is more critical than the total amount consumed. The authors emphasize that persons should be encouraged to increase their plant protein intake to potentially decrease their risk of death. The study also suggests that the underlying mechanisms and active compounds in plant protein that are responsible for this association warrant further investigation. This study contributes to the growing body of evidence supporting the health benefits of plant-based diets and provides valuable insights for dietary recommendations aimed at reducing mortality risks. The findings highlight the need for continued research to fully understand the complex relationship between dietary protein sources and long-term health outcomes. The results underscore the potential benefits of incorporating more plant-based protein sources into the diet to promote cardiovascular health and overall well-being.