Final answer:
An athlete consuming a diet rich in meat to build muscle is primarily ingesting proteins, essential for muscle growth and repair.
Step-by-step explanation:
An athlete eating a diet with lots of meat to build muscle is primarily consuming proteins, which are the biomolecules in meat that facilitate muscle growth and repair. Proteins are essential nutrients made up of smaller molecules called amino acids, critical for building body tissue, including muscle fibers. Each protein molecule is a chain of amino acids that folds up into a three-dimensional structure, allowing it to perform specific functions in the body. Ensuring a sufficient protein intake is vital for athletes to obtain the necessary amino acids to build and repair their muscles, which is a key component of their training and recovery.