Usage of が in this paragraph


Once again I have been stumped over the usage of particles in a passage from
my textbook.

> 先生: 最近、アメリカでも魚や豆腐を食べている人が増えてきたらしいです。
>
> 学生: はい。
>
> 先生: アメリカでも、ヘルシーな食べ物[が]{L}人気[が]{L}出てきたということです。

The paragraph continues but I don’t see the point in typing out the rest as it
won’t be relevant. In the fourth line the there are two が‘s. I asked my
japanese friend why this is and if one could be a は, they said it’s definitely
が but they couldn’t explain why. Please if someone could explain why it’s a
double が and maybe a little additional work information that will help me to
use が and は correctly. Thank you !!




There is a concept called [topic-
prominent](https://en.wikipedia.org/wiki/Topic-prominent_language) in
Linguistics field. I think this theory has the key to understand the
difference.

In many cases, you can translate “Nは” to “As for N”, “In case of N”, or “Now
I’m going to talk about N”. It’s like setting a topic.

When you introduce yourself you should use “は” because you have to set the
topic of you.

> わたし **は** 東京出身です
>
> As for me, I’m from Tokyo.

If you use “が” in the former example, it sounds like you aren’t describing
about yourself (probably because of topic-less).

> わたし **が** 東京出身です
>
> I (not him) am from Tokyo.

This sounds natural as long as answering for a question like “Who is from
Tokyo?” or “Mike is from Tokyo, isn’t he?” This is not to introduce “myself”
but to clarify a contrast, difference or misunderstanding.

One important point here. To understand the difference between は and が, we
have to clarify the difference between “introducing” and “describing (from 3rd
party’s view)”.

> (1) マイク **は** 日本語を勉強している
>
> (1) (We’re going to talk about Mike,) he studies Japanese.
>
> (2) マイク **が** 日本語を勉強している
>
> (2) Mike studies English.

(1) sounds like introducing Mike. So if you were asked “What did you see in
the library?”, _マイク **は** 日本語を勉強していた_ is bad because now the topic is “what
you saw” and not “Mike”. _わたしが見たの **は** マイク **が** 勉強しているところです_ is perfect
instead.

(2) has no topic. It sounds like describing Mike from 3rd party’s view. So if
you were asked “What did Mike do yesterday?”, _マイク **が** 日本語を勉強していた_ is bad
because it sounds like irrelevant story from “what Mike did”. Obviously
started to talk about “Mike” so _マイク **は** 日本語を勉強していた_ is good.

> (3) 人気 **が** 出てきた
>
> (3) It’s getting popular.
>
> (4) 人気 **は** 出てきた
>
> (4) As for popularity it’s getting better. (But sales is not good…)

(3) is very common. we usually talk about “popular things”. When you want to
set “healthy food” as a topic, you can say _ヘルシーな食べ物 **は** 人気 **が** ある_. You
can also say _ヘルシーな食べ物 **が** 人気 **が** ある_ it sounds more like describing
healthy food fairly.

On the other hand (4) is not common because we usually don’t specifically
refer to “the popularity of something”. So it has strong meaning like “As for
popularity” or “In case of popularity”. Thus in this case (4) leads to
contrasting effect against the example of "わたし **が** 東京出身です".

Conclusion. In your example I don’t think _ヘルシーな食べ物 **は** 人気が出てきた_ is bad.
Because they have already talked about healthy food like fishes and tofu. So
it’s natural to set “healthy food” as next topic by using “は”.  
However _ヘルシーな食べ物 **は** 人気 **は** 出てきた_ this is probably also possible but it
sounds confusing because topic is multiple. If you want to emphasize the
contrast against ‘sales’ for example, you can say _ヘルシーな食べ物 **の** 人気 **は**
出てきた_.

