If you’ve added some extra pounds and think a high-protein diet is a better way to manage your weight, think again. Numerous studies show that consuming excess animal proteins such as meat, milk, and cheese has significant health consequences and should give enthusiastic Paleo, Atkins, and other dieters reason for pause.

Such is the case with the latest research out of the University of Southern California’s Davis School of Gerontology. In a study, professor Valter Longo, director of the Longevity Institute at USC, and his colleagues analyzed data from 6,318 American adults ages 50-65 taking part in the National Health and Nutrition Examination Survey (NHANES) III, a strategic effort to assess health and diet status in the U.S.

First, researchers categorized participants into three groups—a “high-protein” group (20 percent or more), a “moderate-protein” group (10 to 19 percent), and a “low-protein” group (less than 10 percent)—based on calorie intake from all protein sources. On average, 16 percent of total daily calories were obtained from protein, while two-thirds of those calories came from animal protein.

Then, investigators compared disease and death rates between groups during an 18-year period.

According to study results published in the journal Cell Metabolism, researchers found that people who ate a diet rich in animal proteins were more than four times as likely to die of cancer as those who ate a low-protein diet. In fact, researchers were surprised that consuming a high protein diet during middle age provided nearly the same risk of dying from cancer as smoking!

Additionally, those who consumed diets high in animal proteins were several times more likely to die of diabetes, as well as 74 percent more likely to die prematurely from any cause.

Interestingly, only seniors (65 years and older) benefited from consuming moderate to high amounts of protein, as these higher levels seemed to protect against diseases like cancer, as well as early death.

The source of protein is most important

Also, researchers found that plant-based proteins—like those derived from beans, nuts, and seeds—did not seem to have the same negative impact on mortality as animal proteins. In fact, the link between high-protein intake and risk of cancer disappeared almost entirely when considering participants whose protein was derived primarily from plants. Additionally, controlling for the amount of carbohydrate and fat intake did not seem to alter cancer or death rates, suggesting that excess animal proteins were indeed the culprit.

While the CDC recommends 46 grams of protein for women and 56 grams for men daily, Longo cautions that “The majority of Americans are eating about twice as much protein as they should, and it seems that the best change would be to lower the daily intake of all proteins but especially animal-derived proteins.”