The Shulchan Aruch (89/4) says that if you won’t be able to have kavana unless you eat or drink, you are allowed to do so. The Mishna Brura (26) says that the Shulchan Aruch specifically says “allowed” as opposed to “required” since nowadays most people don’t have so much kavana in any case. Therefore, you are not required to eat or drink in this case, but you are allowed to.
If it’s Shabbos morning before davening, there are different opinions regarding whether or not you have to make kiddush first. The halacha is also different for a lady who is not makpid to daven every day (I think that everyone would say that she needs kiddush, at least if she already fulfilled her her “shevach, bakasha, hodaah” obligation.)