He wasn't kidding but He was speaking metaphorically. The wine and bread represented His blood and body. They were to drink and eat this together for it was ushering in a new covenant with His sacrifice on the cross. When He warned the Disciples about the "leaven of the Pharisees", He wasn't speaking of gluten but of their teachings. Really, you should read the Bible more then you would know this already.
“the “leaven of the Pharisees” Great point!!! He was using metaphor then and in the Upper Room. They would have caught the metaphor immediately in the Upper Room because not too many days before He had taken the time to explain the metaphor of the Pharisee’s leaven, and these Jewish men knew that for all their generations they were to never drink the blood.
No He wasn't..."THIS IS MY BODY" is not the same as this bread represents My body....transubstantiation is one of the most important, and easily understood truths of Catholicism that Protestants cannot seem to come to grips with......very sad, you are missing out on so very much.