The style of this sentence is poor for three reasons: 1) contains phrases that do not modify any obvious thing 2) Overuses present participles 3) it is hard to understand Let's discuss each point: #1: What does the phrase "when I research a lot" modify? Possibilities are "lunch", "keep", "all day", and "researching". Since "lunch" is located adjacent to the phrase, that would be my first interpretation but I don't think that is what was intended. Sentences should be written in a way that renders obvious what each phrase modifies. #2: The present participles "researching" and "having" are not optimal choices. It would be better to say "research" instead of "keep researching" and "without lunch" instead of "without having lunch". Because of language differences, Asian language speakers need to be especially careful about this. They almost always use too many present participles. #3: I really don't know what this sentence means. I do not understand it. The ideas of doing research all day long and having a limited time seem to contradict each other. Possibly "when" is a bad word choice. It does not create a logical connection between thoughts. Expressions like "because", "in spite of", or "even though" might be better but I cannot say which because I don't know what your intended meaning is.

I make it a rule to research all day without eating lunch when I have to go through lots of documents within a limited time. The other answers are good too. This is just another way to say the same thing. It's you're choice if you want to say ''having lunch'' or ''eating lunch''. Saying ''lots'' is more compact than ''a lot of''.

No, it doesn't sound natural. Here's a more natural version: "I make it a rule to research all day without having lunch when I have to go through a lot of documents in a limited time."

Hi Noboru, The sentence is understandable but could be made more natural. Here’s a revised version: "I make it a rule to research all day without taking a lunch break when I need to go through a lot of documents in a limited time." all the best, Harry