I thought protein as a supplement was only good for building muscle. How does it benefit skin, hair and nails?

Protein is the building block for all your body's cells, including skin, hair and nails, which are often the first cells to suffer if protein is insufficient. In times of low nutritional protein, the body prioritises the repair and maintenance of deeper organs, often reducing the rate of repair of skin.

 

When there is inadequate nutritional protein, such as in many calorie restrictive or vegetarian diets, the body will catabolise (break down) the least used tissues and those not essential for survival, to supply the protein requirements of the vital organs and systems. This often includes deeper skin tissue, and muscles not used or exercised regularly, such as some back muscles.