Spirulina is a blue-green algae and is believed to be one of the oldest life forms on Earth. First used by the Aztecs to increase endurance, spirulina is considered a superfood – an all-encompassing source of nutrients, including protein levels comparable to eggs. The Aztecs also used spirulina to treat various diseases, and legends say that the messengers of the kingdom used the algae to sustain their marathon runs. Modern research supports many of the purported benefits of taking spirulina and continues to study its potential for treating health problems. Spirulina has a bitter taste, so people often mix it with yogurt, juice, and smoothies to enhance the flavor. Spirulina is widely available as a dietary supplement in health food stores.