Eating lunch at your office desk is a bad idea. I know you think you are saving time, or impressing the boss with your work ethics. but research shows that your ability to think critically is compromised when you work and eat at the same time. Not to mention, how your brain gets fried and you don't even taste what you are eating!
On your lunch break, get away from your desk and eat your lunch in a different area (preferably outside, weather permitting). You can focus on your food, clear your head, and get prepared for the rest of the day. I have found that some of my best ideas come to me when I step away from my work.
Yes, you have a job to do, but your most important job is taking good care of yourself.