Eating more protein from plant sources was associated with a lower risk of death and eating more protein from animals was associated with a higher risk of death, especially among adults with at least one unhealthy behavior such as smoking, drinking and being overweight or sedentary, according to an article published online by JAMA Internal Medicine.
The consideration of food sources is critical to better understanding the health effects of eating protein and fine-tuning dietary recommendations.
Mingyang Song, M.D., Sc.D., of Massachusetts General Hospital and Harvard Medical School, Boston, and coauthors used data from two large U.S. studies that had repeated measures of diet through food questionnaires and up to 32 years of follow-up. They examined hazard ratios (risk) for all-cause and cause-specific mortality in relation to eating animal protein vs. plant protein.
Among 131,342 study participants, 85,013 (64.7 percent) were women and the average age of participants was 49. Median protein intake, measured as a percentage of calories, was 14 percent for animal protein and 4 percent for plant protein.
The authors report:
- After adjusting for major lifestyle and dietary risk factors, every 10 percent increment of animal protein from total calories was associated with a 2 percent higher risk of death from all causes and an 8 percent increased risk of death from cardiovascular disease death.
- In contrast, eating more plant protein was associated with a 10 percent lower risk of death from all causes for every 3 percent increment of total calories and a 12 percent lower risk of cardiovascular death.
- Increased mortality associated with eating more animal protein was more pronounced among study participants who were obese and those who drank alcohol heavily.
- The association between eating more plant protein and lower mortality was stronger among study participants who smoked, drank at least 14 grams of alcohol a day, were overweight or obese, were physically inactive or were younger than 65 or older than 80.
- Substituting 3 percent of calories from animal protein with plant protein was associated with a lower risk of death from all causes: 34 percent for replacing processed red meat, 12 percent for replacing unprocessed red meat and 19 percent for replacing eggs.
- Limitations include the study's observational design, so residual confounding (other mitigating factors) cannot be excluded.
"Substitution of plant protein for animal protein, especially from processed red meat, may confer substantial health benefit. Therefore, public health recommendations should focus on improvement of protein sources," the study concludes.