Diet and exercise go hand in hand to aid in weight loss. In order to maximize your chances of developing those killer abdominals you desire, altering your diet is a necessary step.
It is important to remember that weight loss is not instantaneous, nor is it an overly fast process. Healthy weight loss is important, so be sure to do it properly, by adopting a healthy diet as opposed to using dangerous measures such as weight loss pills and fad diets. Ensure you do not adopt these measures as they can be dangerous and will usually result in a person losing significant amounts of lean body mass and muscle.
People who are in jobs that require a lot of sitting, like an office job find it difficult to stick to their eating plans and often end up putting on weight in such environments. I believe there are a few reasons for this namely: Lack of planning, Habit, Boredom and Peer pressure.