It’s natural for anyone trying to lose weight to want to lose it very quickly. But evidence shows that people who lose weight gradually and steadily (about 1 to 2 pounds per week) are more successful at keeping weight off. Healthy weight loss isn’t just about a “diet” or “program”. It’s about an ongoing lifestyle that includes long-term changes in daily eating and exercise habits. To lose weight, you must use up more calories than you take in. Since one pound equals 3,500 calories, you need to reduce your caloric intake by 500—1000 calories per day to lose about 1 to 2 pounds per week.
SOURCE: Centers for Disease Control