After the fall, vegetables were added to the diet: “And you shall eat the herb of the field” (Genesis 3:18). Due to the curse of sin, there was a partial change in diet due to the fact that the quantity and quality of grains and nuts and fruits originally given to man were reduced to such an extent that man would need to supplement his diet with the eating of herbs for a portion of his daily food. This change may also have been due in part to the loss of certain elements from the tree of life, to a change in climate, and perhaps most of all to man’s sentence to hard labor in the process of earning a livelihood.
After the flood, with the temporary destruction of all plant life and the exhaustion of the food supplies that were taken into the ark, an emergency arose that God met by giving permission to eat the flesh of animals. The Lord said, “Every moving thing that lives shall be food for you. I have given you all things, even as the green herbs” (Genesis 9:3). Not that man then first began to eat animal flesh, but only that God for the first time allowed him to.
This permission did not imply an unlimited eating of every kind of animal. If that were the case, many animals would have gone extinct as they entered the ark two by two. However, the clean animals went in by pairs of seven (Genesis 7:1, 2). The first four books of the Bible were written by Moses, and he chose to elaborate on the definition of clean and unclean animals later on in Leviticus 11 and Deuteronomy 14.
So, from the above it can be concluded that Adam and Eve were definitely vegetarian.
In His service,