Animal and plant protein intake and all-cause and cause-specific mortality: results from two prospective US cohort studies

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 risk of mortality

Design

Prospective cohort study

Setting

Health professionals in the United States

Participants

85,013 women and 46,329 men from the Nurses’ Health Study (1980–2012) and Health Professionals Follow-up Study (1986–2012)

Exposure

Animal and plant protein intake as assessed by regularly updated validated food questionnaires

Main outcomes and measures

Hazard ratio (HR) of mortality

Results

The median intake, as assessed by percentage of energy, was 14% for animal protein (5 ^th–95 ^th percentile: 9–22%) and 4% for plant protein (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% confidence interval [CI], 1.01–1.16, P _trend=0.04), whereas plant protein was associated with lower mortality (HR=0.90 per 3%-energy increment, 95% CI, 0.86–0.95, P _trend<0.001). These associations were confined to participants with at least one of the unhealthy lifestyle factors based on smoking, heavy alcohol drinking, overweight or obesity, and physical inactivity, but not evident among those without any of these risk factors ( P _interaction<0.001). Replacing animal protein of various origins with plant protein was associated with lower mortality. In particular, 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, and 0.81 (0.75–0.88) from eggs.

Conclusions and relevance

Higher animal protein intake was positively, whereas plant protein was inversely, associated with mortality, especially among individuals with at least one lifestyle risk factors. Substitution of plant protein for animal protein, especially from processed red meat, was associated with lower mortality, suggesting the importance of protein source.