The statement that is TRUE about protein is:
Excess protein is stored by the body as fat.
While protein is essential for muscle repair and growth, consuming it in excess does not lead to a proportional increase in muscle mass and can result in excess protein being converted to fat for storage. The other statements have inaccuracies. For instance, while protein is important for muscle growth, simply increasing protein intake alone does not guarantee muscle gain without the stimulus of resistance training. Additionally, excess proteins are not stored as amino acids in muscle tissue, as the body cannot store amino acids in that way. Finally, protein is not the primary source of energy for the body; carbohydrates are typically the main energy source.