90-95% of people who lose weight on a diet gain back the same amount or more within 3 to 5 years. Some of the reasons for this are listed below.

By Restricting Caloric Intake, Diets Slow Down Metabolism
The body becomes highly efficient at conserving calories and storing them as fat. Lowered metabolism increases the likelihood that the dieter gains back even more weight than what was lost when the old eating habits return. Without concurrent work on understanding the emotional reasons behind overeating, eating habits remain entrenched and as soon as they return, so does the weight.

Dieting May Cause Depression
Depriving oneself of food can lead to avoidance of social events. One may give up eating out with friends in order to avoid eating something that is not allowed by the diet. This can lead to depression and binge eating in order to cope with it. If the habit persists, it will offset the prior weight loss.

Most Diets Don't Encourage Lifestyle Changes
Although making temporary changes in eating habits will facilitate weight loss, the weight will be gained back once the diet is over and one reverts to the old eating habits. Permanent weight loss requires permanent changes in eating habits, nutritional choices and levels of physical activity.

Very Low Calorie Diets Cause the Loss of Lean Body Mass
Diets that severely restrict caloric intake promote loss of lean body mass instead of fat. Consequently, one can have normal body weight, but with a high ratio of fat. A "flabby" appearance can result.

In order to secure long lasting weight loss success, permanent  changes in eating habits and levels of exercise are required. Emotional coaching can help you with maintaining a healthy life style.