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Whether you develop cancer or not is not determined by your eating habit(s).

Should I use habit or habits?

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I'd go with "habits." You likely have several eating habits. For breakfast, you might always have cereal. For lunch, you might usually have a sandwich. You might drink coffee throughout the day. When you dine out, you usually have a medium rare steak. And so on.

A quote from Merriam-Webster Online Dictionary: https://www.merriam-webster.com/dictionary/habit

The Origin and Etymology of Habit
The word habit most often refers to a usual way of behaving or a tendency that someone has settled into, as in "good eating habits."

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Thank you so much, mountainhiker.
teacherJapaneating habit(s)

Another possibility is to replace this with diet. You can choose.

anonymousAnother possibility is to replace this with diet. You can choose.

Agreed.

As an aside, if I were writing this sentence, I would want to avoid the two nots in close proximity. So, here are three alternative versions:

  1. Whether or not you develop cancer is not related to your eating habits.
  2. Whether or not you develop cancer is not related to your diet.
  3. Whether you develop cancer or remain cancer free is not related to your diet (or eating habits).
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