Plain language summary
Eating a diet high in protein, particularly from plants, has been linked to improvements in indicators for heart disease. However, links to reduction in heart disease, cancer and death remain controversial. This systematic review and meta-analysis of 32 cohort papers aimed to investigate the associations between dietary protein intake and the risk of death, death due to heart disease and death due to cancer. The results showed that total protein and animal protein intake did not affect the risk of death due to heart disease. However, increased plant protein intake decreased the risk of death from heart disease, and this was apparent from as little as an additional 3% of energy from plant proteins per day. Death from any cause decreased as protein and plant protein intake increased, but animal protein alone had no effect. Death due to cancer was not affected by the amount of dietary protein, animal protein, or plant protein. It was concluded that this study supports the recommendation of higher dietary plant protein in the general population to reduce the risk of death by any cause and death due to heart disease and healthcare professionals could use this study to justify this decision.
OBJECTIVE To examine and quantify the potential dose-response relation between intake of total, animal, and plant protein and the risk of mortality from all causes, cardiovascular disease, and cancer. DESIGN Systematic review and meta-analysis of prospective cohort studies. DATA SOURCES PubMed, Scopus, and ISI Web of Science until December 2019, and references of retrieved relevant articles. STUDY SELECTION Prospective cohort studies that reported the risk estimates for all cause, cardiovascular, and cancer mortality in adults aged 18 or older. DATA SYNTHESIS Random effects models were used to calculate pooled effect sizes and 95% confidence intervals for the highest versus lowest categories of protein intake and to incorporate variation between studies. Linear and non-linear dose-response analyses were done to evaluate the dose-response relations between protein intake and mortality. RESULTS 32 prospective cohort studies were included in the systematic review and 31 in the meta-analysis. During the follow-up period of 3.5 to 32 years, 113 039 deaths (16 429 from cardiovascular disease and 22 303 from cancer) occurred among 715 128 participants. Intake of total protein was associated with a lower risk of all cause mortality (pooled effect size 0.94, 95% confidence interval 0.89 to 0.99, I =58.4%, P<0.001). Intake of plant protein was significantly associated with a lower risk of all cause mortality (pooled effect size 0.92, 95% confidence interval 0.87 to 0.97, I =57.5%, P=0.003) and cardiovascular disease mortality (pooled hazard ratio 0.88, 95% confidence interval 0.80 to 0.96, I =63.7%, P=0.001), but not with cancer mortality. Intake of total and animal protein was not significantly associated with risk of cardiovascular disease and cancer mortality. A dose-response analysis showed a significant inverse dose-response association between intake of plant protein and all cause mortality (P=0.05 for non-linearity). An additional 3% energy from plant proteins a day was associated with a 5% lower risk of death from all causes. CONCLUSIONS Higher intake of total protein was associated with a lower risk of all cause mortality, and intake of plant protein was associated with a lower risk of all cause and cardiovascular disease mortality. Replacement of foods high in animal protein with plant protein sources could be associated with longevity.