on an empty stomach

without eating anything

空着肚子，空腹

You should never go to work on an empty stomach.

你不应该空腹去上班。

You want to do yoga on an empty stomach. If you need a snack before hand, try to give yourself at least an hour, and eat food that you can digest quickly and easily.

在练习瑜伽的时候要保持空腹，如果你真的需要吃些东西，那么给自己一个小时的时间，吃些可以很快而且很容易消化的食物。