Pack a healthy lunch - a low-fat sandwich with fruit or nuts - before you go to work. If you keep that on your desk you are less likely to be tempted by the other food around you in the office.
Be honest with your colleagues. If they bring in a cake and hand it around, tell them you are trying to watch your diet and ask them to keep it away from you. Out of sight is out of mind.
Take time out. If you feel the urge to binge on fatty foods during office hours, go for a walk. The craving should disappear in five to 10 minutes.
Go to the gym. Persuade your boss to let you take an hour out to go to the gym or go swimming, and if necessary make the time up later in
the day.
Watch out for the saboteurs. There is always someone who will try to persuade you to eat fatty foods even when you don't want to, usually because they feel guilty about eating these themselves and want you to share their guilt.