According to the Shulchan Aruch (Orach Chayim 89/4), if you are so hungry or thirsty that you will not be able to have kavana unless you eat or drink, you are allowed to.
Water is okay in any case. So are coffee and tea, although the Mishna Berurah says you can’t add milk or sugar. According to Ishei Yisrael, nowadays everyone does add sugar and milk, and there is what to be someich on.
All of the above applies to all Jews, so MO people are okay if they feel they need to eat in order to be able to daven.