I used to work in an office...for many years. I know it's not the most conducive place for your health and fitness goals.
In the last accounting position I had, my department was responsible for our company candy dish. YES! We had a HUGE candy bowl where it was the job of someone in the accounting department to keep it fully stocked at all times.
Talk about temptation! When I first started working there I gained 8 pounds! Gross. So I took myself off candy and started eating healthy and taking Pilates classes (which then turned into me teaching Pilates...and off I went into a whole new lifestyle...but I digress).
So what can you do while you are at work to help you towards your health goals? First off, drop the candy, cookies, birthday cake and free lunches. They are all junk. Bring your own lunch and conveniently have a "meeting" when birthday cake is being served (or go but just don't partake).
Secondly, STAND UP! A recent study showed that sitting for long periods of time causes changes physiologically within your muscles. You stop breaking up fat in your bloodstream. You start getting accumulations of fat in your liver, your heart and your brain. You get sleepy and you gain weight.
Try to at least stand up every 20 minutes. Get your blood moving and your muscles activated. Even better is to walk to the restroom or take the stairs to another floor. Anything will help more than sitting on your expanding behind!
Small steps lead to big results when taken consistently.