Link: Eating Prior To Prayer

Despite my Chasidic predilections, it always bother me when I see [healthy] people eating before davening. The gemara derives the prohibition from a PASSUK and some hold that it an actual di-oraisa. The Rambam and Shulchan Aruch forbid it etc. etc.

Here is a defense of the custom. 

ואחד האוכל ואחד הנמנע מלאכול ובלבד שיכוון לבו לשמים!