Do high protein diets increase cancer risk?

Sufficient protein consumption is critical for health and longevity. Too little protein in the diet leads to low muscle mass, which in turn is strongly associated with increased mortality risk. We have frequently pointed out why the Recommended Dietary Allowance (RDA) of 0.8 grams of protein per kilogram (kg) of body weight per day is too low, and my team generally recommends a daily intake of at least twice that amount – around 1.6 to 2 grams of protein per kg of bodyweight. Many active individuals and those seeking to build muscle aim for even higher levels of protein intake,¹ raising the question: is there such a thing as too much? 

Mechanistic data on the effects of protein on cellular signaling pathways have led to a hypothesis that excess protein intake promotes the development and progression of cancer, an idea that has been widely spread by advocates for protein restriction. However, the fact that a given hypothesis is mechanistically plausible does not necessarily mean that it is true, and in evaluating how protein intake impacts cancer risk, we must adopt a wider perspective. While randomized trials addressing this question are lacking, combining human epidemiological studies with a closer look at mechanistic studies paints a more nuanced picture of the relationship between protein and cancer.