Proteína vegetal vs proteína animal?

Estudo (observacional) recomenda que se privilegie proteína vegetal (principalmente se se tiver outros maus hábitos):
http://www.cbc.ca/news/health/protein-animal-plant-1.3703209


Citando:

"People who eat more protein from plants and less from animals may live longer even when they have unhealthy habits like heavy drinking or smoking, a large U.S. study suggests.
The findings suggest that when it comes to protein, where it comes from may be just as important as how much people eat, said lead author Dr. Mingyang Song, a researcher at Harvard University and Massachusetts General Hospital in Boston.
"Plants are a better source than animal products," Song said by email.
 
 "If people do have to choose among animal products, try to avoid processed red meat and choose fish or chicken instead," Song added."