While some people are concerned about not getting enough protein, a new study shows that we may have too much. The study, published in Cell Metabolism on March 4, shows that middle-aged people who eat a diet high in animal proteins from milk, meat and cheese are four times more likely to die of cancer than someone who eats a low-protein diet — a mortality risk factor comparable to smoking.
Researchers looked at 6,318 adults over the age of 50, over a span of 18 years. On average, about 16 percent of their total daily calories came from protein. Two-thirds of that amount was from animal protein. The percent of calorie intake from protein was used to categorize subjects into a high protein group (20% or more of calories from proteins), a moderate protein group (10%-19% of calories from proteins), and a low protein group (less than 10% of calories from proteins).
The study showed that those consuming high protein diets were 74 percent more likely to die of any cause within the 18-year study period than their low-protein counterparts. They were also several times more likely to die of diabetes. This risk was higher in those who got their protein from animal sources such as meat, eggs and cheese.
“There’s a misconception that because we all eat, understanding nutrition is simple. But the question is not whether a certain diet allows you to do well for three days, but can it help you survive to be 100?” study co-author Valter Longo, Edna M. Jones professor of biogerontology at the USC Davis School of Gerontology and director of the USC Longevity Institute in Los Angeles, said in a press release. “Almost everyone is going to have a cancer cell or pre-cancer cell in them at some point. The question is: Does it progress?” Longo said. “Turns out one of the major factors in determining if it does is protein intake.”
In the study, Longo and his colleagues found that foods derived from plants, such as beans and nuts, did not have the same effect on mortality as did high-protein foods from animals. The results indicate that respondents ages 50-65 consuming moderate to high levels of animal protein display a major increase in the risks for overall and cancer mortality; however, the risks may be somewhat decreased if protein does not come from an animal source. When the study controlled for the effect of plant-based protein, there was no change in the association between protein intake and mortality, indicating that high levels of animal proteins promote mortality.
“The research shows that a low-protein diet in middle age is useful for preventing cancer and overall mortality,” wrote co-author Eileen Crimmins, the AARP Chair in Gerontology at the University of Southern California, in a release about the paper.
Older subjects in the study, however, saw a different outcome from eating a high-protein diet. The researchers found that older subjects (65 years and older) benefited from a moderate to high amount of protein. In this age group in the study, higher levels of protein protected against cancer, disease and premature death.
The RDA for protein is .8 grams per kilogram or 2.2 pounds of body weight. That means if you weigh 140 pounds, the suggested protein intake is 50.9 grams daily. According to myplate.gov a non-active female aged 31-50 requires 1800 calories daily, or 203.6 calories (9%) from protein, which qualifies as low protein.
Ready to reduce or give up the animal products? Here’s a great list of plant based protein sources. I’d add to that my favorite protein source hemp seeds, which provide 10 grams of protein in 3 tablespoons.