Leveling Up, By Only Eating! is a Manga/Manhwa/Manhua in english language, Fantasy series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

The main character is stricken by a rare condition that affects only two people in the entire world, bulimic deficiency. He organizes his daily meals to survive, but his hope of survival grows dimmer as the days go by. He consults a doctor, who suggests playing the Alternate Reality Game ‘Athens’, where he can eat as must as he wants without gaining any weight. He plays the game to save his life and grow in strength by doing nothing but eating! A Gourmet Fantasy Life!