Quick answer
A bright look from another person gladdens the heart, and good news reaches all the way to the bones. Encouragement is physical.
Read both lines
The first line is about a face, probably the face of someone glad to see you, and the effect travels inward to the heart, which reverses the direction of 15:13 where the heart moved outward to the face. Between the two verses the chapter has drawn a circuit: what is in you shows on your face, and what is on your face lands in someone else. The second line makes the claim bodily, and the NKJV footnotes "healthy" as literally fat, which was the ancient picture of thriving rather than an insult; good news puts marrow back in a person. This is the same anthropology as 3:8 and 4:22, where wisdom's effects reached the flesh. Proverbs will not let encouragement be filed as a merely emotional service.
Related: Proverbs 15:13 · Proverbs 17:22 · Proverbs 12:25
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.