Losing weight requires a negative energy balance -- a state in which you expend more energy than you take in through food. It takes a 3,500-calorie deficit to lose 1 lb. of fat, so you need to accumulate a negative energy balance of 35,000 calories to lose 10 lbs. Losing 10 lbs. over the course of three weeks will be difficult, as it requires a negative energy balance of about 1,700 calories a day. The most effective way to lose weight is through a combination of diet and exercise.
Calculate Caloric Needs
You can create a diet plan once you know how many calories your body requires to maintain its weight. Most adults need about 2,000 calories a day. If you did not increase the amount you exercise, the only way you would reach your weight-loss goal of 10 lbs. in three weeks is to consume about 40 calories a day -- an insufficient amount to live. You can use an online calorie calculator to determine your daily energy needs.
Diet
The maximum amount of calories you want to cut from your diet each day is about 500. Anything beyond that can result in nutrient deficiencies, dehydration and unhealthy losses in muscle tissue, rather than fat. Plan on eating about 500 fewer calories each day than your body requires, which translates to about 170 fewer calories per meal. You can also increase your metabolism by dividing these calories into about five or six smaller meals.
Exercise
You'll really have to amp up your physical activity level to burn off the remaining 1,200 calories each day. Vigorous exercise, such as running, rowing and cycling burns about 12 calories per minute. Therefore, you'll need to exercise for about 1 hour and 40 minutes each day at a vigorous level to achieve your weight-loss goal. You can break this time up into two or three smaller exercise sessions as well.
Precautions
Rapid weight loss comes with some risks. When restricting calories, pay attention to eating a variety of foods to ensure adequate nutrient, vitamin and mineral intake. Avoid restricting fat intake -- a popular trend with many diets. Too little fat in the diet can lead to organ damage and reduced hormone production. Regardless of total caloric intake, 20 to 35 percent of your calories should come from fat. Make sure to talk with your doctor before beginning any new diet or exercise program.
References
- "Essentials of Strength Training and Conditioning"; Thomas R. Baechle and Roger W. Earle (editors); 2008
- Rockwell Fitness: METs Common Physical Activity Chart
- MayoClinic.com: Healthy Diet: End the Guesswork With These Nutrition Guidelines
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