What is glycogen and what is its function?

Glycogen is a polysaccharide that serves as the primary form of stored glucose in the body, particularly in the liver and muscle tissues. Its main function is to provide a readily accessible source of energy during physical activity and periods of fasting. When the body requires energy, it can rapidly break down glycogen into glucose, which can then be used by cells for energy production. This process is especially important during exercise, where quick access to energy is crucial.

In contrast, dietary fiber primarily aids digestion and does not function as a glucose store. Proteins, while important for muscle growth and repair, have a different structure and function compared to glycogen. Lastly, although fats are indeed energy storage molecules, they serve a distinct purpose in the body and are metabolized differently than carbohydrates like glycogen. Thus, the correct answer highlights the role of glycogen as a vital energy reserve that supports physical performance and bodily functions.