Have you ever wondered why someone asks you whether you have had your lunch at 4:00pm in the afternoon? Well, it’s the Chinese way of asking you “how are you”. That is why.
A: 你(nǐ)吃(chī)了(le)吗(ma)？ Have you eaten?
B: 吃(chī)了(le)。Yes, I have.
or: 还(hái)没(méi)。Not yet.
The origin of this line goes back to the olden days where food was not as abundant as it is today, so people use this when they want to show that they care for you.