Step 1:
Eliminate salt from your diet. Salt is one of the biggest culprits in water retention. The more salt you eat, the more water you retain, making your belly look fatter than it really is. Stop adding salt to your food and read nutrition labels to look for sodium content. Avoid convenience foods, which are often high in salt.
Step 2:
Drink water throughout the day. Drinking water serves two purposes -- it helps reduce your appetite and helps avoid water retention. Refill your water bottle throughout the day.
Step 4:
Limit refined carbohydrates and junk foods. If you want to lose belly fat in one week, you shouldn't eat junk foods. In addition to having unnecessary salt, they also offer empty calories, which don't fill you up. Stick to whole grains, such as brown rice and whole wheat pasta, or avoid grains altogether.
Step 5:
Exercise every day. A week is a short time, so commit to strenuous exercise to reach your goal. An hour of intense cardio will help you burn calories and sweat out some of your water. Just be sure to drink water to replace what comes out in the sweat or your body will be dehydrated. You'll also want to work on your ab muscles, which will help you stand taller and look slimmer. Do exercises that focus on each area of the abs -- upper, lower and obliques.