Spirulina, which is blue-green algae high in protein, vitamins and minerals, may be an immune booster of sorts, as a number of animal studies point to spirulina's ability to stimulate both antibody and cellular types of immunity. Spirulina guards digestive health and is shown to encourage the growth of beneficial intestinal bacteria needed to balance the GI tract.
Personally, I enjoy spirulina for its antioxidant and anti-inflammatory benefits. The algae's high levels of evercetin and phycocyanin have been shown to alleviate respiratory ailments and aid inflammation associated with joint pain and backache. In addition, high levels of carotenoids in spirulina guard cell health and protect vision.
Many vegans and vegetarians have made spirulina their primary source of protein. The blue-green superfood contains both essential and nonessential amino acids and is similar in structure to animal protein, so it's great for lean muscle building and maintaining healthy weight.