How does the glue of bamboo cutting boards get in the food and how to prevent this?
While it is impossible to prove a negative, I am unable to locate any credible evidence that there is actual danger from glue in bamboo cutting boards.

Consider that even if (and this seems unlikely) there were formaldehyde in the glue in a cutting board that in order to pose a danger it would have to:


Not be bound permanently or chemically modified as the glue cures, 
somehow diffuse through the bamboo to the surface,
transfer into the food in the brief time the food is in contact with the board, and
do so in sufficient quantities as to cause harm.


I would not worry about this in the slightest.