Which statment best decribes how a catalyst can speed up a chemical reaction

Ghrelin.

Ghrelin is a factor that decreases satiety (or increase food intake). It's known as the "hunger hormone" because it's secreted by ghrelinergic cells in the gastrointestinal tract. When the stomach is empty this hormone is secreted and when the gastric walls stretch, because of the food inside, it stops being released.