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 not associated with all-cause mortality (HR, 1.02 per 10% energy increment; 95% CI, 0.98-1.05; P for trend = .33) but was associated with higher cardiovascular mortality (HR, 1.08 per 10% energy increment; 95% CI, 1.01-1.16; P for trend = .04). Plant protein was associated with lower all-cause mortality (HR, 0.90 per 3% energy increment; 95% CI, 0.86-0.95; P for trend < .001) and cardiovascular mortality (HR, 0.88 per 3% energy increment; 95% CI, 0.80-0.97; P for trend = .007). 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 cardiovascular mortality and high plant protein intake was inversely associated with all-cause and cardiovascular 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 prospective cohort study, published in JAMA Internal Medicine, investigated the association of animal and plant protein intake with all-cause and cause-specific mortality among US health care professionals. The study utilized data from the Nurses’ Health Study (1980-2012) and the Health Professionals Follow-up Study (1986-2012), encompassing a total of 131,342 participants. Animal and plant protein intake were assessed through regularly updated food frequency questionnaires. The primary outcomes measured were hazard ratios (HRs) for all-cause and cause-specific mortality. Data analysis was conducted from June 20, 2014, to January 18, 2016. The research aimed to determine the relationship between different protein sources and mortality risks, focusing on the potential health outcomes associated with varying dietary protein choices. The study considered factors such as major lifestyle risks and dietary habits to analyze the impact of animal and plant protein on mortality, providing a comprehensive perspective on dietary protein sources and their effects on health.
Key Findings & Statistics
- Of the 131,342 participants, 85,013 were women (64.7%) and 46,329 were men (35.3%) with a mean age of 49 years.
- The median animal protein intake was 14% of energy (5th-95th percentile, 9%-22%), while the median plant protein intake was 4% of energy (5th-95th percentile, 2%-6%).
- Animal protein intake was not associated with all-cause mortality (HR, 1.02 per 10% energy increment; 95% CI, 0.98-1.05; P for trend = .33).
- Animal protein intake was associated with higher 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 all-cause mortality (HR, 0.90 per 3% energy increment; 95% CI, 0.86-0.95; P for trend < .001).
- Plant protein intake was associated with lower cardiovascular mortality (HR, 0.88 per 3% energy increment; 95% CI, 0.80-0.97; P for trend = .007).
- 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 HRs for all-cause mortality were 0.88 (95% CI, 0.84-0.92) from unprocessed red meat.
- The HRs for all-cause mortality were 0.81 (95% CI, 0.75-0.88) from egg.
- In the 2 cohorts with 3,540,791 person-years of follow-up, there were 36,115 deaths: 8,851 due to CVD, 13,159 due to cancer, and 14,105 due to other causes.
- Plant protein intake was associated with lower all-cause mortality (HR per 3% increment: 0.90; 95% CI, 0.86-0.95; P < .001).
- Plant protein intake was associated with lower cardiovascular mortality (HR per 3% increment: 0.88; 95% CI, 0.80-0.97; P = .007).
- Among participants 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).
- The substitution of 3% energy plant protein was associated with 17% lower mortality due to cancer (95% CI, 7%-27%).
Other Important Findings
- Associations were mostly present in participants with at least one unhealthy lifestyle factor.
- Replacing animal protein with plant protein was linked to lower mortality rates.
- The relationship between animal and plant protein intake and mortality differed based on lifestyle factors.
- The substitution of plant protein for animal protein, particularly from processed red meat, was associated with lower mortality.
- In the unhealthy-lifestyle group, the positive association between animal protein and mortality and the inverse association between plant protein and mortality were more pronounced.
Limitations Noted in the Document
- The study acknowledges that as an observational study, residual confounding cannot be entirely excluded.
- The study population had a moderately higher protein consumption compared to the general US population, which limits assessing the effect of very low intake.
- The study relies on self-reported data, which may introduce some degree of measurement error.
- Dietary assessments were conducted through food frequency questionnaires, which, while validated, may not capture the precise dietary intake.
- The study cannot definitively establish causation due to its observational nature.
Conclusion
The study concludes that high animal protein intake is associated with increased cardiovascular mortality, whereas high plant protein intake is linked to lower all-cause and cardiovascular mortality. These associations are particularly evident in individuals with at least one lifestyle risk factor. The substitution of plant protein for animal protein, especially from processed red meat, was associated with lower mortality, suggesting the importance of protein source. The study supports the notion that dietary recommendations should prioritize the improvement of protein sources, emphasizing the benefits of plant-based proteins. The findings suggest that the long-term health outcomes are influenced by the choice of protein sources, with plant protein offering a favorable alternative to animal protein. The study emphasizes the need to consider the broader dietary context and food source selection when evaluating the health effects of protein intake. The association of plant protein with lower mortality, especially for those with unhealthy lifestyles, further underscores the potential health benefits of shifting towards plant-based diets. The research implies that public health efforts should focus on promoting plant-based protein sources to improve long-term health outcomes.