Eating something without brushing cause any damage to our body?

Hi,
One of my friend didn't paste at all, he just hate to paste and this addiction was from his childhood. He wake up early in the morning at start eating everything without brushing. I wan't to know that without brushing for a decade didn't cause any harm to our body. If your answer is yes then please let me know as soon as possible and if your answer is no then why the doctors are advertising all the time that you must brush your teeth before sleeping in the night and when you wake you should brush your teeth first.

IMO,

Its actually more important to brush before sleep because residual of food may cause cavity in your teeth, and why to do brush in morning ?.. just to get rid of bad smell :P

Rest I don't think it can cause much problem to body as if you have good immune system you can digest all .. I really mean ALL ... even venom of snake (you may feel dizzy for most)..