Spirulina, a protein-dense green algae, is suitable for vegans because it's a robust source of vitamin B12. It's usually available in a powdered form. Not only is Spirulina packed with iron and vitamin A, it's also used in some cases to combat anemia and malnutrition. For maintaining a healthy brain, heart, digestive tract, lungs, and liver, Spirulina can be consumed either as a powder or in tablet form. Moreover, it's simple to mix a bit into a green smoothie or an acai bowl.