Gastric hormones are programmed to restore fat stores after weight loss. The appetite stimulating hormone ghrelin remains high after weight loss, while hunger suppressing hormones, peptide YY and leptin, remain low. Lower leptin levels also lower one’s metabolism. The end result is more hunger and a lower metabolism.
According this NY Times article, this state of more hunger and lower metabolism lasts a long time. A quote:
“Preliminary research at Columbia suggests that for as many as six years after weight loss, the body continues to defend the old, higher weight by burning off far fewer calories than would be expected.”
Well, it’s no wonder; a study that examined 60 years of trials found the common dieting outcome is weight regain or trivial loss.