I'm hungry; I'm starving
A very casual, masculine-leaning expression used among close friends or family. Literally 'stomach has decreased', it conveys a strong, immediate hunger. Not used in polite or formal contexts.
Ah, I'm hungry. Wanna go grab something to eat?
I haven't eaten anything since morning, I'm seriously starving.
Colloquial contraction of 腹が減った (hara ga hetta), literally 'stomach has decreased'. The verb 減る (heru) means 'to decrease' or 'to become empty', and the phrase is a direct, physical way to express hunger.