Bad Protein by Jerry Brainum 1/25

 

In 2014, a study in the Cell Metabolism journal left bodybuilders and those interested in increased longevity bemused. The study said that consuming a higher protein diet significantly increased the risk of early mortality from several causes. Such information was contrary to popular beliefs about a high-protein diet, which was considered healthy. The 2014 study suggested that a high protein diet, defined as eating 20% or more of calories as protein, was dangerous because a higher protein intake promoted a greater release of insulin-like growth factor-1 or IGF-1 and insulin. While both IGF-1 and insulin are considered anabolic hormones (although insulin is primarily anti-catabolic), studies have linked IGF-1 to increased incidence of several types of cancer, and animals and humans born with defective cell receptors for IGF-1 never get cancer or diabetes. Still, they have a higher incidence of cardiovascular disease because, among other functions, IGF-1 helps maintain heart muscle cells. The researchers who published the low protein study suggest that a primary reason why calorie restriction diets that reduce daily caloric intake by 30% or more prolong life is because such diets are lower in protein. However, all of the data show that the effect involves animals. There is scant evidence that consuming a calorie restriction diet in humans will have the same impact on longevity as in animals. Indeed, some aging researchers think it will only work for humans if it begins during infancy, which is hardly practical since that would result in many other problems, such as blunted growth and development.

The 2014 study analyzed a dietary survey of 6,381 American men and women over 50. These people were divided into three groups: 1) High protein, featuring an intake of 20% or more protein; 2) Moderate protein, with 10 to 19% protein intake; and 3) Low protein, with a protein intake of 10% or less of daily caloric intake. Using questionable statistical methods, the study authors found that those in the higher protein group showed a 73-fold increased risk of dying from diabetic complications. Indeed, subjects in the high protein group between ages 50 and 65 showed a 74% increase in mortality from any cause and a four-fold increase in death from cancer. Those with moderate protein intake still showed a three-fold higher risk of cancer death.

In a random sampling of 2253 individuals, IGF-1 levels were positively associated with protein intake, and the authors were able to predict that for every ten ng/ml increase in IGF-1, the mortality risk for cancer increases by 9%. To verify the link between protein intake, IGF-1, and cancer risk, the authors implanted tumor cells into mice on high- or low-protein diets and found that serum IGF-1 concentrations were 35% higher—and that tumors grew faster and 78% larger—in animals on the high-protein diets. When tumor cells were . . .