I don't believe much in calorie counting, but the thing that I do is to avoid food with a lot of sugar and if ever I'll eat a lot, I make sure that I'll be able to normalize everything through exercising.
Most workplaces will really make you eat a lot and fast since you need to be on the go since there are deadlines that need to meet so the best option for you is to exercise afterwards, or before going to work, exercise first.
There's nothing to believe or not to believe, if your calorie intake is smaller than average for your build then you'll lose weight. Junk food, sweets and sitting are the killers here and people tend to combine all of them together.