That was John the Baptist’s diet. Jesus fasted for 40 days and nights, eating nothing.
FASTING
The word (tsuwm) never occurs in the Pentateuch. The Mosaic law, though directing minutely the foods to be eaten and to be shunned, never enjoins fasting.
(from Faussets Bible Dictionary, Electronic Database Copyright © 1998, 2003, 2006 by Biblesoft, Inc. All rights reserved.)
Thats interesting. Doesnt seem to be any single formal definition of what fasting was supposed to be... other than, per Jesus, not to be something you put on display to impress folks about what an awesome faster you are.
Isa 58:3-4
Why have we humbled ourselves, and you have not noticed?' "Yet on the day of your fasting, you do as you please and exploit all your workers. 4 and in striking each other with wicked fists. You cannot fast as you do today and expect your voice to be heard on high.
NIV
3 'Why have we fasted,' they say, 'and you have not seen it?