Whatever one eats reveals the internal appetite of his/her stomach. It reveals what the person was thinking about in terms of food, what the person was desiring to satisfy their hunger cravings.
It seems that the same could be said of the soul -- the immaterial part of humanity where the will, mind, and emotions reside. Whatever one feeds into his/her soul reveals the desires of one's mind and heart. Then, it begins a cycle -- the more we feed it that "thing", usually the "more" we desire that "thing".
And, certainly, there is an internal battle going on for the Christian. We've been "born again to a living hope through the resurrection of Jesus Christ from the dead". We've been "quickened" by the Spirit of God from being "spiritually dead". And, yet there is still a "tendency" for our souls to crave the "passions of our former ignorance", that is our life without God and apart from God's supernatural intervention. God, in his great work, gives us a "new heart" with God-directed desires and impulses through the presence of the Holy Spirit in our lives. Yet again, there is a battle for the feeding of our soul -- that which is "soul-nourishing" vs. "soul-desensitizing" and ultimately "soul-destroying".
Think about the chemical reactions in the brain when we eat sugar -- think Krispy Kreme donuts. Yeah, when the "hot donuts now" sign is lit. When you eat just one...there is a chemical reaction in your brain that says, "give me more, give me more!" If you keep eating the donuts, what happens...you have to eat more to get your "sugar fix" -- it's the exact same thing for a drug addict...same part of the brain, same chemical reaction. Continuing to eat "sugar" foods in this manner will begin to destroy one's appetite for things that are healthy and good for one's physical body.
If we feed our souls "spiritual junk food", our soul will begin to "crave" more and more of that "spiritual junk food" -- like a sugar craving in the brain. We might still "live", but we are desensitizing and destroying our soul and it's desire for the spiritual food that our soul truly needs -- the food of God's Word.