I have heard that ''hate'' is a word which has a negative meaning. Yes, this is true. Therefore, the sentence ''She hates eating fast food'' also has a negative meaning. Yes. This is also true. Because of that the tag question of this sentence is 'does she?' . Is it correct? No. This is not correct at all. You have unfortunately misunderstood the most basic point concerning the rules of negative and positive sentences. The key issue is not about whether the meaning is positive or negative , but about whether the GRAMMAR is positive or negative. "She hates fast food" is a grammatically positive sentence; "She doesn't hate fast food" is a grammatically negative sentence. You need to forget about whether the idea in the verb seems to be positive or negative, and focus on the grammatical structure of the sentence : in other words, whether there is a 'not' in the sentence. It is the presence or absence of a grammatically negative word ( such as 'not' ) in the base sentence which will determine whether the tag question ( or short answer response) is negative or positive. So, following this rule, if the base sentence is grammatically positive, shouldn't the tag be negative? Shouldn't the correct question be "She hates fast food, doesn't she?". Yes, it should. At least, that's what you'll find in any intermediate grammar book in the section on question tags. However, what most grammar books (and many teachers) won't tell you is that not all question tag structures follow the 'positive + negative' and 'negative + positive' format. In fact, we also have 'positive + positive' constructions. There are actually situations where "She hates fast food, does she?" would be a correct construction. You can read about them here: https://www.dailystep.com/en/blog/positive-statements-positive-question-tags

Yes, I think you're right that we probably use tag questions less often in the US. At least, saying "right?" sounds a bit more casual, whereas saying "didn't you," "wasn't it," "aren't we," etc. makes the speaker sound a little more emphatic or serious. And yes, now that you mention it, "huh?" does work just the same as the ++ tag. I'd never thought about it before. Interesting!

Thank you for this comment, Gray. That's interesting. My impression is that tag questions are less of a feature of American English altogether. As I understand it, most AmE speakers would probably just add a 'Right?' to a statement rather than a conventional +/- or -/+ conjugated tag, and (if I'm not mistaken) a 'Huh?' as the equivalent of our ++ tag.

Su.Ki. has explained it well. "Hate" is a negative emotion, but "I hate this" is not a grammatically negative sentence. A grammatically negative sentence must include the word "not" or the word "never" (or a contraction of "not," such as "didn't," "can't," etc.). (As Su.Ki. says, in some places, it's also possible to say "She hates fast food, does she?" This form is never used in the US, though. To me it sounds very British.)

'hate' only has a negative meaning in the sense you dislike something intensely. Is it negative if she tells us 'she hates fast food' ? Not really. She is simply saying she intensely dislikes it. It may be interpreted as a negative comment by someone selling fast food :) but for anyone else, she is just telling us her opinion.