hakike ga aru toki ha, muri ni taberukoto ha nai.

In Japanese, many physical symptoms are expressed with X がある, literally there is X.

So:

• 吐き気がある = to have nausea
• 熱がある = to have a fever
• 痛みがある = to have pain

Here, が marks 吐き気 as the thing that exists.

A learner might expect something more like 吐き気をある, but ある does not take を here. It describes existence, not a direct object.

You may also hear 吐き気がする. That also means to feel nauseous, but 吐き気がある sounds very natural in medical or practical advice.

とき means time or when.

The clause before it modifies it:

• 吐き気があるとき = when you have nausea / when you feel nauseous

Then は marks that whole time-expression as the topic or situation being discussed:

• 吐き気があるときは、... = As for when you feel nauseous, ...

So は is not attached just to とき by itself in meaning; it marks the whole condition 吐き気があるとき.

You could think of it as setting the scene:

• When you feel nauseous, ...

無理 means something like:

• beyond one’s limits
• unreasonable
• forced
• against what is natural or comfortable

With に, it becomes adverbial:

• 無理に食べる = to eat by forcing yourself / to force yourself to eat

This に works like the -ly idea in English for some words:

• 静かに = quietly
• 丁寧に = carefully/politely
• 無理に = forcibly / against one’s limits

So 無理に describes how the eating is done.

Here, こと turns the verb into a noun-like phrase.

• 食べる = to eat
• 食べること = eating / the act of eating / to eat as a thing being discussed

This is important because the sentence uses the pattern:

• verb dictionary form + ことはない

That pattern means:

• there is no need to ...
• you don’t have to ...

So:

• 食べることはない = there is no need to eat / you don’t have to eat

In this sentence, because of 無理に, the sense is more specifically:

• there is no need to force yourself to eat

Yes, literally it can feel strange if you break it apart word by word.

But V-る + ことはない is a set grammar pattern. It means:

• there’s no need to V
• you don’t have to V

So it is better to learn ことはない here as a whole expression rather than trying to translate each piece separately every time.

Examples:

• 急ぐことはない = there’s no need to hurry
• 心配することはない = there’s no need to worry
• 無理に食べることはない = there’s no need to force yourself to eat

This is advice, not a strict ban.

They are similar, but not identical in nuance.

• 食べなくてもいい = it’s okay not to eat
• 食べることはない = there is no need to eat

ことはない often sounds a little more like advice, judgment, or reassurance. It can feel slightly more formal or written than なくてもいい.

In this sentence:

• 無理に食べることはない

has the nuance:

• You don’t need to force yourself to eat
• There’s no reason to make yourself eat

So it is not just permission; it is advice.

Because they are doing different jobs.

1. 吐き気があるときは

   • The first は marks the situation/topic: when you feel nauseous

2. 食べることはない

   • The second は is part of the structure that highlights the action and gives the meaning there is no need to eat

Japanese can stack topic/contrast markers like this when they apply to different parts of the sentence.

A very literal way to feel the structure is:

• As for when you have nausea, as for forcing yourself to eat, there is no need.

That sounds awkward in English, but it shows why both は can appear.

Grammatically, yes: ない is the negative counterpart of ある.

So at a literal level:

• 食べることはない = as for eating, it does not exist

But in real usage, this becomes the established pattern:

• V-ることはない = there is no need to V

So while it is built from the negative of ある, you should understand the whole phrase as an idiomatic grammar pattern.

Yes, in a sentence like this, English may translate it as either when or if, depending on what sounds natural.

• 吐き気があるときは、...
  • When you feel nauseous, ...
  • If you feel nauseous, ...

Japanese とき literally means when / at the time that, but in general advice it often overlaps with English if.

So the sentence is giving guidance for that situation whenever it happens.

Yes. The plain-style sentence is:

• 吐き気があるときは、無理に食べることはない。

A more polite version could be:

• 吐き気があるときは、無理に食べることはありません。

Or more naturally in everyday polite speech:

• 吐き気があるときは、無理に食べなくてもいいです。

The original plain form is common in written advice, instructions, health information, and explanatory text. It is not necessarily rude; it is just less conversationally polite.

Yes, you could.

Both are natural, but they feel slightly different:

• 吐き気がある = to have nausea
• 吐き気がする = to feel nauseous

In many situations, they are very close in meaning.

Very roughly:

• ある can sound a bit more matter-of-fact or clinical
• する can feel a bit more like describing the sensation itself

So:

• 吐き気があるときは、無理に食べることはない。
• 吐き気がするときは、無理に食べることはない。

Both work, and both would be understood easily.