Daniel talked it over with the attendant who had been appointed by the chief official to look after Daniel, Hananiah, Mishael, and Azariah.
"Test us for ten days on a diet of vegetables and water," Daniel said.
"At the end of the ten days, see how we look compared to the other young men who are eating the king's rich food. Then you can decide whether or not to let us continue eating our diet."
So the attendant agreed to Daniel's suggestion and tested them for ten days.
At the end of the ten days, Daniel and his three friends looked healthier and better nourished than the young men who had been eating the food assigned by the king.
So after that, the attendant fed them only vegetables instead of the rich foods and wines.
God gave these four young men an unusual aptitude for learning the literature and science of the time. And God gave Daniel special ability in understanding the meanings of visions and dreams.
When the three-year training period ordered by the king was completed, the chief official brought all the young men to King Nebuchadnezzar.
The king talked with each of them, and none of them impressed him as much as Daniel, Hananiah, Mishael, and Azariah. So they were appointed to his regular staff of advisers.
In all matters requiring wisdom and balanced judgment, the king found the advice of these young men to be ten times better than that of all the magicians and enchanters in his entire kingdom.
Daniel remained there until the first year of King Cyrus's reign.
References for Daniel 1:21