Quick answer
God actively sustains the righteous and frustrates the appetite of the wicked. A statement about the LORD's ongoing government of the world, observed as a pattern; not a contract clause that no believer will ever go hungry.
Read both lines
Notice who the subject is. Most proverbs in this chapter watch how life works; this one names the LORD as the one working it, sustaining in the first line and casting away in the second. The sages did not believe in an automatic universe; deed and consequence grow together under God's active care. And the second line aims at "the desire of the wicked," the craving itself: God does not merely withhold the object, He thwarts the grasping.
What it does not mean
Held as a promise with terms, this verse breaks against reality and then breaks the person holding it, because righteous people have starved, and famine does not check credentials. The proverb states the grain of God's government, and Proverbs is honest that the pattern has exceptions this side of the end (13:23). What it refuses to allow is the opposite creed: that God is indifferent to whether the righteous eat. That the psalmist could say "I have not seen the righteous forsaken" (Psalm 37:25) tells you the pattern is real; that Paul knew hunger (2 Corinthians 11:27) tells you it is a pattern, not a contract.
Related: Proverbs 13:25 · Proverbs 13:23 · Matthew 6:31–33
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.