Keeping weight off is notoriously difficult, and a small new study sheds light on why it's so hard: To truly keep the pounds away, people may have to deal with feelings of increased hunger for the rest of their lives. The study, from researchers in Norway, involved 34 patients with "severe" obesity who weighed 125 kilograms, on average, at the study start. The individuals participated in a rigorous, two-year weight-loss program involving diet and exercise, during which they lost about 24 lbs. (11 kg) on average. Participants were able to keep their weight off for this two-year period, but their levels of the hunger hormone ghrelin increased, and those increases lasted for the entire study. What's more, participants also experienced increases in their feelings of hunger, and these feelings never went away.