http://en.wikipedia.org/wiki/Protein [2]
http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/ [3]
http://en.wikipedia.org/wiki/List_of_types_of_proteins [4]
Links[1] https://hootsgo.org/?q=node/6315 [2] http://en.wikipedia.org/wiki/Protein [3] http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/ [4] http://en.wikipedia.org/wiki/List_of_types_of_proteins