Abstract
Importance Defining what represents a macronutritionally balanced diet remains an open question and a high priority in nutrition research. Although the amount of protein may have specific effects, from a broader dietary perspective, the choice of protein sources will inevitably influence other components of diet and may be a critical determinant for the health outcome. Objective To examine the associations of animal and plant protein intake with the risk for mortality. Design, Setting, and Participants This prospective cohort study of US health care professionals included 131 342 participants from the Nurses’ Health Study (1980 to end of follow-up on June 1, 2012) and Health Professionals Follow-up Study (1986 to end of follow-up on January 31, 2012). Animal and plant protein intake was assessed by regularly updated validated food frequency questionnaires. Data were analyzed from June 20, 2014, to January 18, 2016. Main Outcomes and Measures Hazard ratios (HRs) for all-cause and cause-specific mortality. Results Of the 131 342 participants, 85 013 were women (64.7%) and 46 329 were men (35.3%) (mean [SD] age, 49 [9] years). The median protein intake, as assessed by percentage of energy, was 14% for animal protein (5th-95th percentile, 9%-22%) and 4% for plant protein (5th-95th percentile, 2%-6%). After adjusting for major lifestyle and dietary risk factors, animal protein intake was weakly associated with higher mortality, particularly cardiovascular mortality (HR, 1.08 per 10% energy increment; 95% CI, 1.01-1.16; P for trend = .04), whereas plant protein was associated with lower mortality (HR, 0.90 per 3% energy increment; 95% CI, 0.86-0.95; P for trend < .001). These associations were confined to participants with at least 1 unhealthy lifestyle factor based on smoking, heavy alcohol intake, overweight or obesity, and physical inactivity, but not evident among those without any of these risk factors. Replacing animal protein of various origins with plant protein was associated with lower mortality. In particular, the HRs for all-cause mortality were 0.66 (95% CI, 0.59-0.75) when 3% of energy from plant protein was substituted for an equivalent amount of protein from processed red meat, 0.88 (95% CI, 0.84-0.92) from unprocessed red meat, and 0.81 (95% CI, 0.75-0.88) from egg. Conclusions and Relevance High animal protein intake was positively associated with mortality and high plant protein intake was inversely associated with mortality, especially among individuals with at least 1 lifestyle risk factor. Substitution of plant protein for animal protein, especially that from processed red meat, was associated with lower mortality, suggesting the importance of protein source.
Generated Summary
This research article, published in JAMA Internal Medicine, presents a prospective cohort study investigating the relationship between animal and plant protein intake and the risk of mortality in a large population of US healthcare professionals. The study utilized data from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS), encompassing over 130,000 participants, with follow-up periods extending up to 32 years. The primary objective was to examine how the choice of protein sources—animal versus plant—influences health outcomes, specifically focusing on all-cause and cause-specific mortality. The researchers employed validated food frequency questionnaires to assess protein intake, analyzing data from 2014 to 2016. The study’s design allowed for the assessment of long-term dietary patterns and their association with mortality risks, considering various lifestyle and dietary factors. The approach involved using Cox proportional hazards regression models to estimate hazard ratios (HRs) and assess the impact of substituting different protein sources on mortality. The study aimed to provide insights into the optimal dietary composition concerning protein sources and their implications for public health recommendations.
Key Findings & Statistics
- The study included 131,342 participants, with 85,013 women (64.7%) and 46,329 men (35.3%). The mean age was 49 years.
- The median protein intake, assessed by percentage of energy, was 14% for animal protein and 4% for plant protein.
- Animal protein intake was weakly associated with higher mortality, particularly cardiovascular mortality (HR, 1.08 per 10% energy increment; 95% CI, 1.01-1.16; P for trend = .04).
- Plant protein intake was associated with lower mortality (HR, 0.90 per 3% energy increment; 95% CI, 0.86-0.95; P for trend < .001).
- These associations were confined to participants with at least 1 unhealthy lifestyle factor based on smoking, heavy alcohol intake, overweight or obesity, and physical inactivity.
- Replacing animal protein with plant protein was associated with lower mortality.
- The HRs for all-cause mortality were 0.66 (95% CI, 0.59-0.75) when 3% of energy from plant protein was substituted for an equivalent amount of protein from processed red meat.
- The HR was 0.88 (95% CI, 0.84-0.92) when substituting for unprocessed red meat.
- In the 2 cohorts, 36,115 deaths were documented, with 8,851 due to CVD, 13,159 due to cancer, and 14,105 due to other causes.
- The study documented 36,115 deaths, of which 8,851 were due to CVD, 13,159 were due to cancer, and 14,105 were due to other causes.
- Higher intake of animal protein was associated with higher CVD mortality.
- The multivariable HR per 10% increment of animal protein intake from total energy intake was 1.02 (95% CI, 0.98-1.05; P for trend = .33) for all-cause mortality and 1.08 (95% CI, 1.01-1.16; P for trend = .04) for CVD mortality.
- The multivariable HR per 3% increment of total energy intake of 0.90 (95% CI, 0.86-0.95; P for trend < .001) for all-cause mortality and 0.88 (95% CI, 0.80-0.97; P for trend = .007) for CVD mortality.
- The HR for all-cause mortality was 0.66 (95% CI, 0.59-0.75) when 3% of energy from plant protein was substituted for processed red meat; 0.88 (95% CI, 0.84-0.92) from unprocessed red meat; 0.94 (95% CI, 0.90-0.99) from poultry; 0.94 (95% CI, 0.89-0.99) from fish; 0.81 (95% CI, 0.75-0.88) from egg; and 0.92 (95% CI, 0.87-0.96) from dairy.
Other Important Findings
- The associations between protein intake and mortality were modified by lifestyle factors. The positive association of animal protein with all-cause mortality and the inverse association for plant protein intake were restricted to the unhealthy-lifestyle group.
- In the unhealthy-lifestyle group, the multivariable HR per 10% increment of animal protein was 1.03 (95% CI, 0.99-1.07; P for trend = .16) and the HR per 3% increment of plant protein was 0.90 (95% CI, 0.85-0.95; P for trend < .001).
- When stratified by history of diabetes, the positive association with all-cause mortality for animal protein intake and the inverse association for plant protein intake appeared to be stronger among participants with diabetes than those without diabetes.
- The study found that the substitution of plant protein for animal protein, particularly from processed red meat, was associated with lower mortality.
- High animal protein intake was associated with a higher risk for CVD mortality.
Limitations Noted in the Document
- The study acknowledges that the protein consumption in the study population was moderately higher than in the general US population.
- As an observational study, the possibility of residual confounding could not be excluded.
- The study’s observational nature limits the ability to establish definitive causal relationships.
- The reliance on self-reported dietary data, which may be subject to measurement error.
- The study was limited to healthcare professionals in the US, which may limit the generalizability of the findings to other populations.
Conclusion
The findings underscore the importance of protein source in relation to long-term health outcomes. High intake of animal protein was associated with increased mortality, especially in individuals with unhealthy lifestyles. Conversely, higher intake of plant protein was associated with lower mortality. The most impactful finding was that substituting plant protein for animal protein, particularly from processed red meat, was associated with a substantial reduction in mortality risk. These results suggest a shift towards plant-based protein sources as a strategy for improving health outcomes. This supports the idea that the public health recommendations should focus on the improvement of protein sources. This highlights the need to prioritize the quality of protein sources in dietary guidelines, emphasizing the potential benefits of incorporating more plant-based protein into the diet, especially replacing processed red meat. The findings advocate for dietary strategies promoting the substitution of plant-based proteins for animal proteins, particularly from processed red meat sources, to reduce mortality risk. The study supports the growing body of evidence suggesting that focusing on the source of protein can provide significant health benefits. Therefore, public health recommendations should focus on the improvement of protein sources, favoring those from plants to improve long-term health and longevity.