Legumes, and especially soybeans, are an abundant source of natural protease inhibitors, according to the book “Pathology for the Health Professions” by Dr. Ivan Damjanov 1. Some research suggests that protease inhibitors found in soybeans may play a role in soy’s anti-cancer properties, according to Damjanov, and may help protect against certain cancers such as breast and colon. The particular protease inhibitor found in soy, called Bowman-Birk, appears to help prevent tumor formation, according to “Pathology for the Health Professions
Another natural source of protease inhibitors is the potato, according to a review published in the June 2009 issue of the International Journal of Molecular Sciences 2.
Antioxidant compounds in green tea called catechins produce protease-inhibiting activity, according to a study published in the April 2003 edition of the journal Antiviral Researchhealthfully List of Natural Protease Inhibitors