prepositions - What is the difference between "in" and "for" in "hasn't eaten in five months"?

Now the cubs are growing, fed on mom's milk, but mom herself hasn't eaten in five months, and is getting thinner by the day.

What does in mean here, and how would the meaning of that piece change if for were used?

Answer

I found two similar questions in the English Language & Usage section: [1], [2].

It seems that in and for may be used interchangeably in negative sentences, although in positive sentences only for is correct. The use of in in such cases is more common in American English.