A new study suggests a higher risk of death accompanies consumption of animal protein, compared with eating plant-based protein.
Dr. Mingyang Song - from the Massachusetts General Hospital and Harvard Medical School in Boston - and colleagues publish their work in JAMA Internal Medicine.
They note that protein sources "inevitably influence other components of diet, including macronutrients, micronutrients, and phytochemicals, that can in turn influence health outcomes."
As such, they say accounting for food sources is of extreme importance in better understanding the health effects of different types of protein.
Previous studies have promoted vegetarian diets for their health benefits, while others have cautioned against meat consumption for potential health risks.
A recent study, for example, suggested that a vegetarian diet reduces the risk of type 2 diabetes. Meanwhile, another study suggested red meat consumption is linked to kidney failure.
To further investigate, Dr. Song and colleagues examined data from two large studies in the United States that used repeated measures of diet through food questionnaires as well as 32 years of follow-up.
Eating more plant protein linked to lower risk of death
In total, there were 131,342 study participants, 64.7 percent of whom were women; the average participant age was 49.
The researchers examined risk for all-cause and cause-specific mortality in light of eating animal protein versus plant protein. Additionally, they adjusted for major lifestyle and dietary risk factors.
Results showed that every 10 percent increase in animal protein from total calories was linked with a 2 percent higher risk of death from all causes and an 8 percent increased risk of death from cardiovascular disease.
This increased risk of death linked to eating more animal protein was more noticeable among the study participants who were obese and those who drank larger quantities of alcohol.
Interestingly, eating more plant protein was linked with a 10 percent lower risk of death from all causes for every 3 percent segment of total calories and a 12 percent lower risk of death from cardiovascular disease.
Additionally, the link between eating more plant protein and lower risk of death was stronger among the participants who smoked, drank at least 14 grams of alcohol per day, were overweight or obese, were physically inactive, or were younger than 65 or older than 80.
Commenting on their findings, the researchers write:
"Although substituting plant foods for various animal foods was associated with a lower mortality, red meat, especially processed red meat, showed a much stronger association than fish and poultry, which themselves were not associated with mortality."
"In fact," they add, "protein from certain fish, such as cod, has been suggested to improve the lipid profile, glycemic control, and insulin sensitivity."
'Recommendations should focus on improvement of protein sources'
The researchers also discovered that substituting just 3 percent of calories from animal protein with plant protein was linked with a lower risk of death from all causes.
Despite the strengths of the large sample size, repeated dietary assessments, and high follow-up rate, the team points to some limitations.
Firstly, the study population had a moderately higher protein consumption compared with the general U.S. population, which limits the researchers' ability to examine effects of the very low end of animal protein intake.
Additionally, because this is an observational study, they could not exclude residual confounding, which is the distortion that can remain even after controlling for confounding factors. However, the researchers say their "results are robust."
"Substitution of plant protein for animal protein, especially from processed red meat, may confer substantial health benefit," they conclude. "Therefore, public health recommendations should focus on improvement of protein sources."