Idiom:
Lines of communication ( way of communication )

Hit the book:
What it means is, there is a tight copulation between food habits and the character/approach.
I agree with this 100%. I tested this on myself and learned. Each and every food has its capability to add certain nature. It is understandable by close observations as well.
I am a human, humans can eat meat.
That meat had to come from some animal, that animal also eats (lets same a few steps and say it eats grass).
The grass needs nutrients too: mostly CO2 and H2O.
So in the end... if that were true: every living thing is what it eats and that would be carbon-dioxide and water.