Quick weight loss isn't easy, but that doesn't mean it's impossible. For 67 percent of Americans, carrying too much weight is a serious health concern, according to the Centers for Disease Control and Prevention. Simply put, it's no easy task to lose 21 pounds in 21 days. But it can be done, if you're willing to put in serious effort.
Make an appointment with your health-care provider to ensure that you are healthy enough to handle the rigors of a 21-day weight-loss plan. Most health insurance plans cover all or part of the cost of an annual physical. Let your doctor know that you are planning an aggressive weight-loss program.
Prepare a meal plan that includes three meals and one snack each day, for a total of 1,200 calories. This is as low as dietitians recommend dropping your daily calorie intake. Making a plan and writing it down will help you stick to it, so be specific about portion size and cross items from your list each day as you finish eating. Be sure you're getting calories from nutrient-rich foods, such as lean meats, no-fat dairy foods and fruits and vegetables, rather than wasting your calorie allotment on low-nutrient foods. If you follow this plan, you can lose two pounds per week.
Get started with a daily one-hour cardiovascular workout. An hour of cardio exercise -- good options for cardio include running and biking, or you can try aerobics or spin classes -- burns around .29 pounds each day. That adds up to about six pounds in a month.
Add another hour of cardio every three days. By burning an extra .29 pounds a couple of times throughout the week, you'll add another two pounds of weight loss.
Don't eat starches. Starchy foods, like potatoes, rice, bread and pasta, naturally soak up your body's water supply, causing you to retain weight. If you completely eliminate them from your diet, you can lose almost six pounds of water weight within a few days.