The amount of protein used in the body is influenced by the percentage that is digestible by the body, and the total quantity of protein fed to the body. Bodybuilding and other strength training promotes the utilization and conservation of protein's amino acids in the body. Using alternate energy sources lessens the amount of amino acids that will be metabolized for energy. An increase of protein in the diet does not lead to greater protein efficiency, more protein will be lost, but a greater amount of protein will be conserved in the body through sheer volume, staying a step ahead of the metabolization of amino acids for energy.
This supposedly happens roughly two days after a water fast, according to fasting proponents.