"For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting." Galatians 6:8
Just as we feed our physical bodies that which is nourishing for health and strength, so too we are to feed our inner man that we might overcome the temptation of sin. However, just as when we eat the wrong foods on a regular basis we suffer the consequences of ill health, so too by not feeding upon the living Bread we can become spiritually weak.
Scripture warns us to not sow to the flesh because what we sow we shall reap. Not only do we suffer consequences for our sin, but we quench the Holy Spirit's working and thereby feel the effects of death in our lives.
Galatians gives us a synopsis of the contrasts between the flesh and the Spirit. By abiding in Christ we will bear the fruits of the Spirit, but if we allow our fleshly lusts to be indulged, we will begin to express the works of the flesh. So be careful what you eat, it may have ramifications you never desired or expected.
"Forasmuch then as Christ hath suffered for us in the flesh, arm yourselves likewise with the same mind: for he that hath suffered in the flesh hath ceased from sin; That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God."1 Peter 4:1-2