Fasting is a practice of discipline; consciously choosing to forgo one thing to focus on another. You don't not eat because God or Allah or Buddha or whomever actually care that you didn't eat. You don't eat to focus on mastering your own desires such that you can better your own mindfulness of adherence to the other strictures of your faith during your daily life, even when you are not fasting.
The reason many religions focus on fasting is that it is a common and simple way to be aware of a temptation and choose to not give into it.
Edit: I should add, in case my point wasn't obvious, that none of the above has to do with you or anyone else. It is purely a personal thing.
Anyone who brags about how much religious fasting they are doing are just showing that they have been wasting their time and have gotten nothing from it.