The root of the word for food is אכל. Bearing other related words in mind, this word implies that food is integrated into the personality of the one who consumes it. We may only eat food that is in line with our personality and does not cause a negative influence.
Only God truly understands our makeup and can determine which foods are allowed to be eaten. Originally, Man was only allowed to eat the seeds of agricultural plants (such as grain) and fruit. Animals were to eat leaves and herbs.
After the flood Man was permitted to eat animals. This may have been an accommodation to the climate changes which limited the availability of grain and fruit.
Beraishis 1:29, Page 37
