BOSTON, Aug. 1 (UPI) -- Studies have been showing for some time that eating too much meat -- especially red meat -- is bad for health, with researchers now reporting that replacing a small amount of animal protein with proteins from plants can reduce the risk of death from all causes.
Replacing 3 percent of dietary protein from animal products with proteins from grains, vegetables or other plants reduces the risk of death regardless of any other unhealthy lifestyle choice, according to a new study published in the journal JAMA Internal Medicine.
Dietary changes considered by Harvard Medical School researchers looked at red meat, processed red meat and eggs, which have been the focus of several studies on healthy changes to diet.
A 2015 study by the World Health Organization suggested processed red meat such as bacon, hot dogs and corned beef can significantly increase the risk for cancer, the researchers in the study noted it was likely that all types of red meat affect the risk.
In an update to dietary guidelines earlier this year, the U.S. Department of Agriculture and U.S. Department of Health and Human Services also acknowledged the risk to health of overconsumption of meat, especially among men and boys.
The agencies recommended red meats be replaced with other sources of protein such as nuts, seeds and seafood, portending what Harvard researchers report in the new study.
Dr. Mingyang Song, a researcher at Harvard Medical School, said that while previous dietary studies have looked at levels of protein compared to carbohydrates, or protein intake on its own, the sources of protein have not been reviewed as closely as in the new study.
"There has been limited study on the differences between proteins, but research in this area can provide the public with important information," Song told UPI in a phone interview. "Food sources of protein are not just about the protein itself, but other nutrients in the food."
For the study, researchers reviewed medical data for 131,342 participants in the Nurses' Health Study and Health Professionals Follow-up Study, assessing animal and plant protein intake based on validated food frequency questionnaires.
The median protein intake among participants assessed as a percentage of energy was 14 percent for animal protein and 4 percent for plant protein.
After adjusting for lifestyle and dietary risk factors, the researchers found that for every 10 percent increment of animal protein in total calories, risk of death increased by 2 percent and risk of death from cardiovascular disease increased by 8 percent.
Conversely, for every 3 percent increment of plant protein in a diet, risk of death decreased 10 percent and risk of cardiovascular death decreased 12 percent.
For less healthy participants -- people who smoke cigarettes, drink at least 14 grams of alcohol per day, are obese, are inactive or at an advanced age -- the effects of swapping out meat protein for plant protein were much higher than for healthier participants.
"We expected the substitution of plant proteins to balance out unhealthy lifestyle aspects, but we did not expect the stronger effects of unhealthy groups," Song said, though he noted that healthier participants consumed more chicken and fish.
"This is one explanation, we think there could be others," Song said. "It's possible that the benefit of plant proteins is more significant among the unhealthy group because these people may have underlying inflammation or other disorders, which could increase the potential benefit of substituting plant proteins."
The study suggests replacing 3 percent of animal protein sources.
The small shift in diet away from animal protein was significant, with the risk of death going down by 34 percent if processed red meat is replaced, 12 percent for replacing red meat and 19 percent for replacing eggs.
Although confirmation of the study's findings is difficult -- Song said you can't ask people to eat only plants or animals for 10 years and follow them to see what happens -- the researchers plan to investigate the mechanism mediating the harm or benefit of different types of protein.
Future research also needs to confirm the study's findings with similarly large analysis of different populations to get a better view of the effects of protein sources on health, Song said.