As any dieter knows, it's hard to keep weight off. Weight regain is a familiar problem for dieters. The research appears in Thursday's issue of the New England Journal of Medicine.

　　To study what drives it, Proietto and his colleagues enrolled 50 overweight or obese patients in Australia in a 10-week diet program.

　　On average, the participants lost almost 30 pounds in the 10 weeks - faster than the standard advice of losing a pound or two per week. Even so, they gained an average of 12 pounds back over the next year.

　　The scientists checked the blood levels of nine hormones known to influence appetite - and found that even a year after the end of the weight-loss program, six of the hormones were still out of whack.

　　People who regain weight should not be harsh on themselves, as eating is our most basic instinct, study author Joseph Proietto of the University of Melbourne in Australia said. It's better not to gain weight than to try to lose it.