Protease inhibitors are induced in all most all plants in response to insect feeding and/or wounding.  Also they are proteins themselves that  are degraded by gastric juices as described above or by heating when the plant is cooked.  Soybean seeds naturally have a lot of them and can affect digestion in some non ruminants such as pigs.   However,  I don't know of any GM plants that are transformed with these genes for insect resistance, because the insects rapidly enlist a new set of digestive proteases that are not affected by the plant protease inhibitors.  It's not likely that they have been approved by federal agencies because of their potential antigenicity to human.

You have a very interesting question. Well let me tell you that trypsin or amylase coding genes not only show polymorphism in the same species but even at intrageneric level. Therefore, some of these inhibitors which work on insects may not affect us at all.

Hi Subin, I think it would depend on the concentrations of these inhibitors in the GM crop.

Amylase is produced by salivary glands and the pancreas. Trypsin is produced by the pancreas. Before ingested food reaches the pancreatic juices, it goes through the stomach where acids denatures proteins and pepsin cleaves them.

Could amylase and trypsin inhibitors survive this? Possibly, but a high concentration of these inhibitors will increase the odds in their favor.

But you have to realize that most of the natural (non-GM) foods we eat every day have amylase and/or trypsin inhibitors in them:

http://www.ebi.ac.uk/interpro/entry/IPR006106

http://www.researchgate.net/publication/221861330

http://www.academicjournals.org/article/article1380100578_Habeeb%20and%20Khalid.pdf

http://www.tandfonline.com/doi/pdf/10.1080/00288233.1979.10420841

http://www.sciencedirect.com/science/article/pii/S0168945204000731

http://www.tandfonline.com/doi/abs/10.1080/87559129009540866#.VC7zqrAtCM8

Article α-Amylase Inhibitors: A Review of Raw Material and Isolated ...

Protease inhibitors are induced in all most all plants in response to insect feeding and/or wounding.  Also they are proteins themselves that  are degraded by gastric juices as described above or by heating when the plant is cooked.  Soybean seeds naturally have a lot of them and can affect digestion in some non ruminants such as pigs.   However,  I don't know of any GM plants that are transformed with these genes for insect resistance, because the insects rapidly enlist a new set of digestive proteases that are not affected by the plant protease inhibitors.  It's not likely that they have been approved by federal agencies because of their potential antigenicity to human.

Thank you everyone ! 

To Dr. Luthe, Actually they have been infact used commercially in combination with the Bt gene (Refer attached publication). Thank you.

Article Prospects for Using Proteinase Inhibitors to Protect Transge...

One should note that there are some differences in insect and human proteases like trypsin, amylase etc. Also in many cases it is evident that one inhibitor can not inhibit trypsin from different sources. There are reports of plant trypsin inhibitors that can inhibit trypsin from fungi but can not inhibit insect trypsin despite of the fact that the inhibitor belongs to the same family of insect trypsin inhibitors. Similar is the case with amylase inhibitors also. Thus crops containing protease inhibitors do not affect us. But higher concentrations of inhibitors may affect the taste, and digestibility

This appears to be less of a problem in the case of human consumption as such crops would be cooked before human consumption, with concomitant protein denaturation and inactivation. However, such crops may also be used as animal feed so that potential differences between uncooked normal and transgenic crops should be evaluated. A study has addressed this issue by feeding rats with transgenic peas expressing high levels of α-AI1 and monitoring possible effects on intestinal metabolism, growth and starch and protein digestibility. The minimal nutritional differences seen up to a dietary level of 300 g per kg of transgenic pea should encourage the use of transgenic crops as animal feed.