http://www.ncbi.nlm.nih.gov/pubmed/9339609
4.Nutritive Value of Foods, United States Department of Agriculture, Agricultural Research Service, Home and Garden Bulletin Number 72. May be accessed at:https://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25w421.pdf and http://www.nal.usda.gov/fnic/foodcomp/Data/HG72/hg72_2002.pdf