It is amazing how odors can get through most odor proof bags.
Humans may not be able to smell the food, but bears, dogs, ... can sure smell it.
One good thing is that it is a very faint smell and so usually isn't strong enough to attract animals from a long distance.
I have heard that a bear can smell when you open a can of tuna from miles away.
So don't pack tuna(or any fish) in bear country:-)
I have also heard that bears have a very good nose for fat of any kind, including vegetable oils that humans have a hard time smelling.