Step 1
Decrease your caloric intake to lose two pants sizes. Additional calories you take in are stored as fat if not used for bodily functions or physical activity. Therefore, reducing the amount of calories you consume will result in fat loss and a reduction in pants size. According to Medline Plus, you must have a 3,500-calorie deficit to lose 1 lb. of fat. If you reduce your intake by 500 calories per day for seven days, you will lose 1 lb. of fat per week. Over three weeks, you will lose 3 lbs. of fat just from dietary changes alone.
Step 2
Choose more low-calorie, vitamin-rich foods to lose two pants sizes in three weeks. As you begin your diet to lose weight, you must build a healthy foundation and learn to consume healthier foods, such as fruits, vegetables, whole grains, legumes, lean meats and low-fat dairy products. If you commit to eating these foods, you might eat larger portions without taking in an excessive amount of calories. Follow the USDA's recommendations, which say half your plate should contain fruits and vegetables, one fourth whole grains and one fourth lean proteins per meal. Avoid high-calorie beverages, such as sodas, juices and sweetened teas.
Step 3
Exercise regularly to burn additional calories to lose two pants sizes. Set a goal to participate in at least 30 minutes per day of aerobic exercise, five to seven days per week. The more aerobic exercise you perform, the more likely you will reach your goal of losing two pants sizes in three weeks. Make sure you exercise at a moderately high to high intensity to burn calories more efficiently. Try speed walking, jogging, biking or swimming. Avoid leisurely aerobic exercise, which might not be as effective in helping you achieve your goal.
Warnings
Check with your doctor before beginning an exercise program, particularly if you have health problems.
Tips
Individuals lose weight at varying rates depending on body type. Be patient in your weight loss efforts. If you improve your diet and exercise habits, you will reach your goal eventually.