This is an excellent and eye-opening habit to get in to.
When most people start out, they don’t have a realistic idea of how many calories they are actually consuming, and where those calories come from.
The best and easiest way I have found to keep track of my eating is with My Fitness Pal http://www.myfitnesspal.com . Try it! Use it! Make sure to record everything. There’s even an iPhone/iPod touch app!!
Pay attention to what types of foods contribute most to your calorie intake, and what time of day you tend to consumer excess calories. Armed with this knowledge, you can continue to use your diary to see if you’re meeting your diet and exercise goals!