Longman, my former professor at RTS, wrote this on his facebook page worth re-quoting here:
I just heard Rick Warren talk about his new book, the Daniel Plan on CBS news yesterday. I applaud his efforts to help us all keep trim. However, citing Daniel’s water and vegetable diet as the model made me chuckle a bit. The look that Nebuchadnezzar was going for was not lean and mean but plump. If you check out ancient depictions of Babylonian wise men, they are bald, round faced and chubby. Daniel was giving God room to work. At the end Nebuchadnezzar thought it was his diet that made Daniel so pleasantly chubby (many cultures even today prize a little girth on people), but Daniel knew that God was in control and made him chubby in spite of his diet. The next chapter shows that it is God’s wisdom and not the Babylonian wisdom that he learned in school that made him truly wise. For more detail see my Daniel commentary (NIVAC; Zondervan).