High Protein Diets Harmful and Unnecessary for Endurance Athletes

By Dr.  John Mcdougall

Level of dietary protein impacts whole body protein turnover in trained males at rest by Patricia Gaine in the April 2006 issue of Metabolism found in five male endurance runners that, “a protein intake of 1.2 g/kg or 10% of total energy intake is needed to achieve a positive nitrogen balance.”  The source of protein was beef and vegetarians were excluded from the study.  No advantage was found for consuming higher levels of protein.  The high protein diet (30% protein, 30% fat, and 40% carbohydrate—like the Zone diet) provided insufficient carbohydrates to replenish muscle glycogen and may result in fluid imbalances and dehydration according to the researchers.

Comment:  Protein is the most “sacred” of all nutrients, especially for athletes—like most people, they are unnecessarily worried about getting enough.   Protein supplements, bars, and shakes many times push these athlete’s diets beyond limits that could be achieved by ordinary eating.  But in the end they fail to benefit and do much harm by believing the “protein means performance” myth.  Performance comes from efficient fuel, and that fuel is carbohydrate.  Furthermore, excess protein can inhibit performance by causing a diuresis which can lead to water loss and a relative condition of dehydration.  Over several years all that protein and associated acid will tear down the bones.

With rice at 8%, potatoes at 10% and beans at 28% protein, along with an abundance of carbohydrate and other essential nutrients, a diet based on plant foods makes ideal nutrition for an endurance athlete.  This is the reason science-based recommendations for physical performers are consistently to make high carbohydrate starches their meal centerpiece—and that is exactly what the winners do.