John Gill 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)

And at the end of ten days their countenances appeared fairer, and fatter in flesh At the time fixed for the trial of them, when they came to be examined, they appeared to be of a better complexion, and a more healthful look, and even plumper and fatter, with good solid flesh, and not swelled up as persons in a dropsy: than all the children which did eat the portion of the king's meat : who appeared at the same time, and were compared with them, being under the care of the same persons:

now this was owing to the blessing of divine Providence, as Jacchiades observes; for, how healthful soever pulse may be, or the several things designed by it, particularly rice, of which Aben Ezra on the place gives great encomiums, as very salutary and nourishing, and a purifier of the blood; yet neither that, nor any of the things before mentioned, tend to make persons fat in flesh, as these were.