Where does the undigested food go?

Undigestive food will either go to your appendix or it will go out the drain. If I understand your question correctly you are asking where does the undigested food go? The answer would be that the body eliminates it with digested waste products. A good example of this is corn. Corn is undigestible by the human body and is eliminated with other waste. Ah yes, Corn: nature's broom.