פּירוש אויף דניאל 1:13

and as you will see According to what you see, do.

And let our appearance and the appearance of the children be pleasing before you. He did not say that they should only have a pleasing appearance, nor did he say that they should be healthier in flesh than those who eat the king's food. For regarding appearance, it depends on the joy of the heart, as stated in Nedarim, page 49b, concerning Rabbi Yehuda, who had radiant countenance even though he was under duress at the time, and also they, in their joy, not to defile themselves, their appearance would be good. However, regarding being healthier in flesh, naturally, vegetarian food does not cause bloating or fattening, and he did not want to rely on miracles. But God, in His mercy, made their appearance better and their flesh healthier than all the children of their age. So wrote from there our Rabbi, Rabbi Moshe Alshich.

[Daniel 1:13] Ve-yera’u (וְיֵרָא֤וּ - And let [our appearance] be seen): [Meaning:] At the end of the ten [days, let] our appearance [be seen and compared]. And he [Daniel] mentioned “the king’s pat-bag [food]” and adopted a concise manner of speaking (derech ketzarah - דֶּרֶךְ קְצָרָה) in that he did not mention the wine [even though they were also abstaining from it].