A reasonable time line for weight loss is to achieve a 10 percent reduction in body weight over 6 months of therapy. After 6 months, this caloric deficit theoretically should result in a loss of 26 to 52 lb. However, the average amount of weight lost actually observed over this time period usually is in the range of 20 to 25 lb. It is difficult for most patients to continue to lose weight after a period of 6 months due to changes in resting metabolic rates and difficulty in adhering to treatment strategies, although some can do so. To continue to lose weight, diet and physical activity goals need to be revised to create an energy deficit at the lower weight, since energy requirements decrease as weight is decreased.
Many studies show that rapid weight reduction almost always is followed by regaining of weight.
Moreover, with rapid weight reduction, there is an increased risk for gallstones and, possibly, electrolyte abnormalities.