Dieters won't lose weight permanently
An analysis of 31 long-term studies that had followed people for between two and five years on a range of diets reveals that people on diet would gain their weight back within five years. From Guardian:
Prof Mann found that although dieters typically lost up to 10% of their starting weight in the first six months, at least one-third to two-thirds of people on diets regain more weight than they lost within four or five years.
Among those who were followed for more than two years, 83% eventually gained back more weight than they lost - one study showed that half of dieters weighed more than 4.99kgs (11lb) more than their starting weight five years after the diet.