After eating from the tree of knowledge [of good and evil], all the animals ate as well, and they were brought to such a low extent that Noah and his sons were permitted to eat as a means to raise the animals up once more. Through eating animals, they become part of the human body, as they nourish us, and so they are raised from the level of animal, of living, to the level of man, of speaking.
However, because of our lowly level, eating doesn't completely rectify the animals back to the level of Gan Eden, for our bodies are on a lower level than the animals of Gan Eden. Which means that we must try with all our might to use the energy and life we get from consuming animals to do HaShem's will, perform mitzwoth, learn Torah, pray, and think holy thoughts. Only in this way can we return the animals to their original level. Otherwise, when we consume animals we become more animal, rather than turning the animal into man, we turn into animals ourselves.