I see that there are concerns regarding hypoglycemia, but it's really only a concern when you are a diagnosed diabetic or if you literally haven't eaten the day when you are riding or the day before. As long as you have eaten enough before you start your long ride, you don't have to force yourself to eat. Of course, it's important to bring something to eat with you that you like just in case, but most of the time, fluids is enough. Your body will definitely feel it when you need to eat, not just your stomach, but you also feel a different feeling like light-headedness or numbness of your extremities, for example, which is different than the normal feeling you get when you are tired.