What is protein? Protein is one of the three macronutrients (the others are carbohydrate and fat) that provides our bodies with energy and is a building block for healthy muscles, skin, hair, and nails. Protein also plays an important role in enzymes, hormones, regulating fluid balance and your body's pH balance. When you break down protein into its smallest form it is made up of peptide bonds and amino acids. There are 20 different amino acids. They are categorized into 3 gr