Blame the hunger hormone ghrelin. Even when an obese person loses a serious amount of weight through exercise and dietary changes, their overall hunger levels go up. The increased hunger might explain why only two out of 10 participants were able to keep their weight down after the study ended. But at each step along the way, researchers quizzed them about their hunger levels. Not only did their subjective hunger levels increase and stay high throughout the two-year trial, but their blood showed higher levels of ghrelin, the so-called \"hunger hormone.\"