You shall keep My decrees and laws, which man shall do, and live in them… (18:5)

Rabbi Yosef Yitzchok of Lubavitch wrote:

When my grandmother, the Rebbetzin Rivkah, was eighteen years old she fell ill and the doctor ordered that she eat immediately upon waking. But grandmother, who did not wish to eat before prayer, would pray at an early hour and only afterwards eat her breakfast.

When her father-in-law, Rabbi Menachem Mendel of Lubavitch, heard of this, he said to her: "A Jew must be healthy and strong. Concerning the precepts of the Torah it is written "live in them"- one is to infuse life into the mitzvos; and in order to infuse life into the mitzvos, one must be fit and joyful."

Concluded Rabbi Menachem Mendel: "Better to eat in order to pray, than to pray in order to eat."