Charles Ellicott Commentary Daniel 1:15

"And at the end of ten days their countenances appeared fairer, and they were fatter in flesh, than all the youths that did eat of the king`s dainties." — Daniel 1:15 (ASV)

Appeared fairer.— Thus was God beginning to assert His power among the Babylonians. This change in the appearance of Daniel was the effect of his free grace, not of the meat that came from the king’s palace. Is it not possible that the young exiles thought of the words of Isaiah (Isaiah 52:11), Depart ye, depart ye, go ye out thence, touch no unclean thing?