Cut out any food that encourages your body to hold onto fat in the midsection. A few primary offenders include alcohol and caffeine. These substances make your body retain water, which often accumulates most at your gut. To get your belly fat down within a week, cutting out these items will help you lose water weight and some of that bloat. Also consider nixing complex carbs from pasta and bread. These foods are hard to process, often leaving fat behind in your body.