Actually we were initially designed without a digestive system at all. Adam and Eve were given a digestive system only after being cast out of the garden of Eden. After being vast out they had difficulty finding nourishment similar to what was available in the garden. God sent an angle to bring them each a fig. The figs were very large. They had no idea how to eat them at first, when they finally did they suffered terrible stomach pains. After that they were put to sleep and their bodies modified for the environment. When they woke up and saw what had been done to their bodies they were devastated. They knew then there would be no returning to Eden,no body designed like their's would ever be permitted entrance. There are many old texts available that speak of these early days of humanity. The Forgotten Books of Eden from the Apocrypha are some of the most easily available online. Can find them on sites such as sacred texts under Apocrypha(means hidden in Greek)
From the Forgotten Books of Eden : God says "O Adam, when thou wast in My garden, thou knewest neither eating nor drinking; neither faintness nor suffering; neither leanness of flesh, nor change; neither did sleep depart from thine eyes. But since thou transgressedst, and camest into this strange land, all these trials are come upon thee."
The first Human hunger.
2 "But when thou camest to dwell in this strange land, thy animal body could not be on earth without earthly food, to strengthen it and to restore its powers."
3 And God withdrew His Word from Adam.
Then they sat down to eat the figs; but they knew not how to eat them; for they were not accustomed to eat earthly food. They feared also lest, if they ate, their stomach should be burdened and their flesh thickened, and their hearts take to liking earthly food.
Adam and Eve acquire digestive organs. Final hope of returning to the Garden is quenched.
AND when it was day, they rose and prayed, after their custom, and then went out of the cave.
2 But as they felt great trouble from the food they had eaten, and to which they were not used, they went about in the cave saying to each other:--
3 "What has happened to us through eating, that this pain should have come upon us? Woe be to us, we shall die! Better for us to have died than to have eaten; and to have kept our bodies pure, than to have defiled them with food."
4 Then Adam said to Eve, "This pain did not come to us in the garden, neither did we eat such bad food there. Thinkest thou, O Eve, that God will plague us through the food that is in us, or that our inwards will come out; or that God means to kill us with this pain before He has fulfilled His promise to us?"
5 Then Adam besought the Lord and said, "O Lord, let us not perish through the food we have eaten. O Lord, smite us not; but deal with us according to Thy great mercy, and forsake us not until the day of the promise Thou hast made us."
6 Then God looked upon them, and at once fitted them for eating food; as unto this day; so that they should not perish.