I get this question a lot from clients who feel totally disconnected from their body and have strayed so far away from normal eating that they are at a loss.  My favorite definition comes from the legendary RD guru, Ellyn Satter:

       Normal eating is going to the table hungry and eating until you are satisfied. It is being able to choose food you like and eat it and truly get enough of it—not just stop eating because you think you should. Normal eating is being able to give some thought to your food selection so you get nutritious food, but not being so wary and restrictive that you miss out on enjoyable food. Normal eating is giving yourself permission to eat sometimes because you are happy, sad or bored, or just because it feels good. Normal eating is mostly three meals a day, or four or five, or it can be choosing to munch along the way. It is leaving some cookies on the plate because you know you can have some again tomorrow, or it is eating more now because they taste so wonderful. Normal eating is overeating at times, feeling stuffed and uncomfortable. And it can be undereating at times and wishing you had more. Normal eating is trusting your body to make up for your mistakes in eating. Normal eating takes up some of your time and attention, but keeps its place as only one important area of your life.
In short, normal eating is flexible. It varies in response to your hunger, your schedule, your proximity to food and your feelings.

Normal thinking about food takes up about 15-20% of your day.  We call this the total conscious time (TCT).  Thinking about food less than this means you're likely not nourishing your body well, and thinking about food more than this constitutes disordered thinking because you're thinking about food more than you need to be.  Interestingly, simply putting a person on a diet will bump their TCT up to ~40-60% as a result of the body feeling deprived.  And a person with a clinical eating disorder will typically report a TCT at 70-100%, which is part of the brain's reaction to semi-starvation.

Take an inventory of your eating and thinking patterns.  If you find yourself falling greatly outside of the normal ranges, you may want to consider a consult with an RD who specializes in disordered eating issues.