Abstract
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 risk of mortality. Design—Prospective cohort study. Setting—Health professionals in the United States.
Generated Summary
This study, published in the JAMA Internal Medicine, investigates the association between animal and plant protein intake and all-cause and cause-specific mortality. It is a prospective cohort study utilizing data from two large U.S. cohorts: the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The study population comprised 85,013 women and 46,329 men, with a mean age of 49 years, followed for an average of 22 years. The primary objective was to examine how different protein sources, specifically animal and plant-based, relate to mortality risks. The research employed a food frequency questionnaire to assess protein intake and used Cox proportional hazards regression models to estimate hazard ratios (HR) and 95% confidence intervals (CI) of mortality associated with different protein intakes. The analysis included adjustments for multiple lifestyle and dietary risk factors. Furthermore, the study performed an isocaloric substitution analysis to examine the effect of replacing animal protein with plant protein from various sources. The findings offer valuable insights into the dietary sources of protein and their impact on long-term health outcomes.
Key Findings & Statistics
- The median intake of animal protein, as assessed by the percentage of energy, was 14% (5th–95th percentile: 9–22%), while plant protein was 4% (2–6%).
- Animal protein intake was weakly associated with higher mortality (HR=1.08 per 10% energy increment, 95% CI, 1.01–1.16, Ptrend=0.04) for cardiovascular mortality.
- Plant protein intake was associated with lower mortality (HR=0.90 per 3% energy increment, 95% CI, 0.86–0.95, Ptrend<0.001).
- For all-cause mortality, HRs (95% CI) were 0.66 (0.59–0.75) when 3% of energy from plant protein was substituted for processed red meat.
- HRs (95% CI) were 0.88 (0.84–0.92) from unprocessed red meat, 0.81 (0.75-0.88) from eggs.
- Participants consuming >18% energy from animal protein had a higher BMI.
- The study documented 36,115 deaths, of which 8,851 were due to CVD, 13,159 to cancer, and 14,105 to other causes.
- Higher intake of animal protein was associated with a HR per 10%-energy increment of 1.08 (95% CI, 1.01–1.16, Ptrend=0.04) for CVD mortality.
- The increased mortality associated with higher animal protein intake was more pronounced among obese participants (Pinteraction=0.008) or heavy alcohol drinkers (Pinteraction=0.06).
- In the unhealthy-lifestyle group, the multivariable HR per 10%-increment of animal protein was 1.03 (95% CI, 0.99–1.07, Ptrend=0.16), and the HR per 3%-increment of plant protein was 0.90 (95% CI, 0.85–0.95, Ptrend<0.001).
- The HRs (95% CI) of all-cause mortality were 0.66 (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 (0.84–0.92) from unprocessed red meat, 0.94 (0.90–0.99) from poultry, 0.94 (0.89–0.99) from fish, 0.81 (0.75-0.88) from eggs, and 0.92 (0.87-0.96) from dairy.
Other Important Findings
- The study found that higher intake of animal protein was associated with higher CVD mortality.
- In contrast, higher plant protein intake was associated with lower mortality.
- Substitution of plant protein for animal protein, especially from processed red meat, was associated with lower mortality.
- The associations between protein intake and mortality were more pronounced in individuals with at least one unhealthy lifestyle factor.
- The study examined the substitution association of different protein sources with mortality and found that protein intake from processed red meat was strongly associated with mortality, whereas no association was found for protein from fish or poultry.
- The study found that the relationship of animal and plant protein with mortality varied by lifestyle factors and any statistically significant protein-mortality associations were restricted to participants with at least one of the unhealthy behaviors, including smoking, heavy alcohol drinking, overweight or obesity, and physical inactivity.
- Compared to the healthy-lifestyle group, the unhealthy-lifestyle group with similar animal protein intake consumed more unprocessed and processed red meat, egg, and high-fat dairy, but less chicken, fish, and low-fat dairy.
Limitations Noted in the Document
- The study’s protein consumption was moderately higher than the general US population, limiting the ability to assess the effect of very low intake.
- The observational nature of the study means residual confounding could not be entirely excluded.
- The study population was composed of educated health professionals, which might limit generalizability to the broader population.
- Study relied on self-reported dietary information, which is subject to measurement error.
- The study was unable to determine causality.
Conclusion
The study concludes that after adjusting for other dietary and lifestyle factors, animal protein intake was associated with higher risk of cardiovascular mortality, whereas higher plant protein intake was associated with lower all-cause mortality. The associations were confined to participants with at least one lifestyle risk factor. The research suggests that the source of protein is an important determinant of health outcomes, and that substituting plant protein for animal protein, especially from processed red meat, may confer a substantial health benefit. The authors emphasize that public health recommendations should focus on improving protein sources. Key findings include that animal protein intake was linked to higher mortality, especially in those with unhealthy lifestyles, while plant protein intake was associated with lower mortality. Moreover, the substitution of plant protein for animal protein, particularly from sources like processed red meat, showed a significant association with reduced mortality risk. This study supports the importance of considering the source of protein in dietary guidelines and underscores the potential health benefits of shifting towards plant-based protein sources.