Proteins are made up of amino acids, which are the building blocks of most of the cells in the human body. Without amino acids, you’d be unable to replace the skin cells you lose every day, grow hair and fingernails, or rebuild and repair damaged muscle tissue. Proteins are essential for optimal health and body functioning. Every gram of protein has four calories. Protein comes from meat, fish, eggs, dairy products, and some lentils, such as soybeans. It’s often consumed as a dietary supplement in powdered form, particularly among those who regularly exercise.