Eating more protein from plant sources was associated with a lower risk of death while eating more protein from animals, particularly red meats, was associated with a higher risk of death, a U.S. study said Monday.

"Overall, our findings support the importance of the sources of dietary protein for long-term health outcomes," said Mingyang Song, a research fellow in the Massachusetts General Hospital and corresponding author of the report.

"Our findings also have public health implications and can help refine current dietary recommendations about protein intake, in light of the fact that it is not only the amount of protein but the specific food sources that is critical for long-term health."

While previous studies have primarily focused on the overall amount of protein intake from a broad dietary perspective, the specific sources of protein are equally important, said Song, whose paper was published in the U.S. journal JAMA Internal Medicine.

Song and colleagues analyzed data from two long-term epidemiologic studies, the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS), which have compiled comprehensive health data on more than 170,000 participants since the 1980s.

In addition to completing overall health questionnaires every two years, participants provide information on their dietary intake -- specifically how often they consumed portions of particular types of food during the preceding year -- every four years.

The researchers analyzed more than 30 years of data for NHS participants and 26 years of data for HPFS participants. During those time periods more than 36,000 deaths were documented among study participants -- almost 9,000 from cardiovascular disease, around 13,000 from cancer and about 14,000 from other causes.

After adjustment for lifestyle and other dietary risk factors, a high consumption of protein from animal sources, any types of meat, eggs or dairy, was weakly associated with an increased rate of death, while high consumption of protein from plant sources, breads, cereals, pasta, beans, nuts and legumes, was associated with a lower mortality rate.

More careful analysis revealed that the association of animal protein intake with an elevated mortality risk only applied to participants with at least one factor associated with an unhealthy lifestyle -- being either obese or underweight, heavy alcohol consumption, a history of smoking, or physical inactivity.

In fact, the association disappeared in participants with a healthy lifestyle. "While we expected we might find the associations to be weaker in the healthy lifestyle group, we did not expect them to completely disappear," said Song.

Analysis based on specific sources of protein indicated that the animal-protein-associated mortality risk applied primarily to processed and unprocessed red meats, which include both beef and pork products, and not to protein from fish or poultry.

"Our findings suggest that people should consider eating more plant proteins than animal proteins, and when they do choose among sources of animal protein, fish and chicken are probably better choices," he added. Endit

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