Twenty pounds is a significant weight loss goal, but it's perfectly achievable if you are patient and disciplined. Most importantly, it's a safe weight loss goal that falls within the Centers for Disease Control and Prevention's recommendation to lose weight at a rate of one to two pounds per week. To shed those unwanted pounds, get active and watch what you eat while maintaining a healthy calorie deficit.
Get 150 to 200 minutes of moderate-intensity exercise per week. According to the Pennington Nutrition Series you can expect to lose weight when you achieve this level of exercise and reduce your calorie intake.
Track the number of calories that you burn using a heart rate monitor when you exercise.
Keep a food diary to track your daily food intake. Write down the foods you eat, when you eat them and the number of calories they contain. This will provide you with insight into your eating habits.
Create a daily 833-calorie deficit between the calories you burn from exercise and by reducing your calorie intake. This means that if you burn 400 calories with exercise you will need to reduce your daily intake by 433 calories to achieve this goal. This will result in weight loss at a rate of 1-2/3 pounds per week -- or 20 pounds in 12 weeks.