People who shed pounds quickly typically rely on extreme exercise programs or very-low-calorie diets, which are tough to maintain for more than a few weeks.

Your doctor may recommend a very low calorie diet if you need to lose weight quickly before a medical procedure or if you have serious health problems because of obesity.

In a small study, 20 severely obese patients who were put on a very low-calorie diet lost an average of 20 percent of their body weight.