Protein is made up of chains of amino acids and is essential for building body tissue. It can serve as a fuel source, containing 4 calories per gram like carbohydrates. Proteins are involved in most bodily functions and processes. They are broken down into amino acids during digestion and some amino acids must be obtained through diet as the body cannot produce them. Not consuming enough protein can lead to muscle wasting and conditions like kwashiorkor characterized by edema and skin issues.