Q. The halacha is that one may not eat before davening,
I am diabetic. A normal morning sugar reading is between 70-100. If my sugar reading is, let’s say, at 300, I am to inject a certain amount of insulin which will help the sugar flowing in my veins to be converted to energy. However, it is not absolutely essential that I do the injection before davening. (In fact, for some reason, maybe lower stress, my sugar reading is always lower after davening.)
Would doing the injection before davening be akin to eating and forbidden?

Similar question. Can one feeding himself by a G-tube connected directly to the stomach (gastrostomy), feed before davening, when there is no medical need to do it then? Can he do it on Yom Kippur? Can someone who chews his food (bolus) and then, because of his difficulty or impossibility of swallowing introduces it to the stomach via a G-tube, also feed before davening or chew the food on Yom Kippur?

A. Horav Shlomo Miller’s Shlit’a opinion is that feeding via a G-tube is not considered eating, therefore no brocho is recited and it may be done before davening or in Yom Kippur when needed, obviously the same applies to an insulin injection.
However, as a matter of principle, ideally one should always try to daven, thank Hashem and pray, before engaging in any activity when possible. The Rov added, that food that is just chewed in the front part of the mouth and then expectorated, does not require a brocho even if later introduced into the stomach via a G-tube. It can as above be done before davening when needed, but should be avoided in Yom Kippur.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a