The analysis of the 32-year Nurses' Health Study, followed by the Health Professionals Follow-Up Study at Harvard University, didn't just look at the diets of the participants over a year. It reviewed them repeatedly — "specifically how often they consumed portions of particular types of food during the preceding year — every four years," a statement said.
Song's team found that a 10 percent increase in proteins from animals resulted in a 2 percent increase in mortality overall, and an 8 percent rise in death risk from heart disease. But a 3 percent increase in protein from plants led to a 10 percent decrease in mortality and a 12 percent drop in risk of death from cardiovascular-related mortality.
The findings are clear, said Song, a research fellow at the hospital's Clinical and Translational Epidemiology Unit: Plant-based proteins from sources such as beans, nuts, quinoa and seeds are a healthier choice than steaks or beef products such as hot dogs. That said, "I wouldn't suggest that everyone switch to vegan," Song added. That's because certain meats — chicken and fish, for example — also carried a much lower mortality risk overall and from heart disease.
But the traditional American diet, rife with animal products such as burgers, meatballs, meatloaf, steaks, eggs and dairy, "is associated with a variety of bad outcomes," Song said.
The research of the two studies started in the 1980s and totaled what the study called "3.5 million person-years." In that time, there were 36,000 deaths among the participants — 13,000 from cancer, 9,000 from cardiovascular disease and 14,000 from a mix of causes.
"After adjustment for lifestyle and other dietary risk factors, a high consumption of protein from animal sources ... was weakly associated with an increased risk of death, while high consumption of protein from plant sources — breads, cereals, pasta, beans, nuts and legumes — was associated with a lower mortality rate," the statement said.
In some cases, it's not just that meat is bad and plants are good. Processed meats are filled with potentially unhealthy additives such as sodium, nitrites and nitrates.
Song said he embarked on the study because while others have suggested health benefits from a plant-based diet, none looked at the source of protein. "We were able to link information over the years," he said. The data from the two large, long-term studies "provided a unique opportunity to look at long-term health outcomes."