How Fast Can You Lose 20 Pounds?

The rate at which you can lose weight depends on the method you use, as do the side effects. For example, you can drop 20 pounds in just a few weeks if you undergo weight-loss surgery. If you follow a crash diet or a similarly high-risk method, you could lose the weight in just over a month. The healthiest strategies of low-calorie, balanced eating and exercise are the smartest choices, but losing 20 pounds this way is likely to take four months or more. Consult your doctor before beginning any weight-loss program.

Diet

It's necessary to burn or cut out 3,500 calories to lose 1 pound, so trimming 1,000 calories from your diet every day without changing anything else will help you lose about 2 pounds per week, or a total of 20 pounds in 10 weeks. Another option is following a very-low-calorie diet, a medically supervised weight loss program in which patients eat 800 or fewer calories per day. According to the Weight-Control Information Network, people who follow very-low-calorie diets may lose weight rapidly --- up to 5 pounds per week or 20 pounds in a month.

Exercise

The amount of weight you can lose through exercise alone depends on how many calories you burn; this, in turn, depends on how much you weigh. For example, the MayoClinic.com website calculates that running at a speed of 8 miles per hour will burn nearly 1,500 calories in 60 minutes if you weigh 240 pounds. An hour of running at that speed every day --- without making other lifestyle changes --- would help you lose about 3 pounds per week, meaning you'd lose 20 pounds in seven weeks.

Surgery

Bariatric surgery is a term that encompasses all types of weight-loss surgery; the most popular type is gastric bypass surgery. According to the MedlinePlus online medical encyclopedia, people who undergo gastric bypass surgery normally lose 10 to 20 pounds in the month following the procedure, making it one of the quickest overall weight-loss methods. However, patients who choose gastric bypass surgery still must diet and exercise to live healthily.

Healthy Methods

Losing weight healthfully involves combining a balanced, low-calorie eating plan and regular exercise. In doing so, you might lose up to 2 pounds per week, or slightly more if you are very overweight. The Centers for Disease Control and Prevention don't recommend losing weight at a faster rate than 2 pounds per week with healthy methods, because the effects of quick weight loss are less likely to last over time.

Risks

There are many risks in losing weight quickly, some very serious. The risks of gastric bypass include anemia, blood loss, heart attack, stroke, vomiting, gallstones and kidney stones. According to the American Heart Association, following a crash diet or unbalanced low-calorie diet for more than a few weeks could lead to nutrient deficiencies. Finally, Dr. Donald Hensrud writes on MayoClinic.com, quick weight-loss methods are rarely sustainable, meaning that you may gain back weight you lose when you return to normal habits. Before starting any weight-loss plan, speak with your doctor and heed his safety advice.