This study, which analyses data from two long-term epidemiologic research studies in the US, found that specific food sources of protein in the diet affected health outcomes in differing ways. Taking into account a number of other dietary and lifestyle factors, the authors showed that animal protein intake was weakly associated with a higher risk for mortality.
This was particularly true for mortality from cardiovascular disease. More specifically, the animal-protein-associated mortality risk applied primarily to processed and unprocessed red meats and not to fish or poultry. Conversely, higher plant protein intake was associated with lower all-cause mortality.
However more detailed analysis showed that the associations of animal protein intake with a raised risk of mortality were limited to participants with at least one factor associated with an unhealthy lifestyle, such as obesity, heavy alcohol consumption, smoking, or physical inactivity. No effect was seen in those with a healthy lifestyle. An examination of the types of animal protein consumed found that the sources of animal protein varies between the healthy and unhealthy lifestyle group: those in the former consumed more red meats, eggs and high-fat dairy, while the latter consumed more fish and poultry.
The authors suggest that the negative effects of high animal protein intake and beneficial effects of plant protein 1) may be increased by other unhealthy lifestyle choices and 2) manifest primarily among the subgroup of individuals with these behaviours who may already have had some underlying inflammatory or metabolic disorders.
The study used data from the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS), two cohort studies with comprehensive health data on more than 170,000 participants over 32 years. All participants in these studies completed health questionnaires every two years starting in the 1980s, and provided detailed information on their diet and lifestyle every four years. Combining this information with mortality data of the participants allowed the authors to assess relationships between protein intake from different plant and animal sources and rates and causes of death. The analysis included controlling for a range of lifestyle factors and used a ‘nutrient density model’ which adjusted for total energy intake and the percentage of energy from various fats.
The paper supports evidence from other epidemiological studies such as the Oxford-led EPIC group, which has a cohort from across 10 European countries with nearly half a million participants (not mentioned in this article). In a paper published in 2013, Rohrmann et al. publish evidence that processed meat contributed to mortality from cardiovascular disease as well as cancer, with some indication that high consumption from red meat may do the same.
In all then, the study seems to indicate that:
- high animal protein intakes are associated with higher risk of mortality; but
- this seems to manifest itself in individuals who have unhealthy lifestyles (in one way or another);
- this may be because much depends on the type of animal protein consumed, with red and processed meat showing this association but fish and poultry not – people who consume higher quantities of meat but who also have healthy lifestyles tend to eat more fish and poultry rather than red or processed meat.
d. Plant protein seems to have beneficial associations with health.
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  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.
Song, M., Fung, T. T., Hu, F. B., Willett, W. C., Longo, V. D., Chan, A. T., & Giovannucci, E. L. (2016). Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA Internal Medicine, doi:10.1001/jamainternmed.2016.4182