Spirulina is a blue-green algae that was a food source for the Aztecs and other Mesoamericans until the 16th century. Spirulina powder is a complete protein containing all essential amino acids, with about 60% total protein. It is also rich in B vitamins and various health-promoting minerals. Due to these properties and its high iron content, spirulina is often supplemented in vegetarian and vegan diets.