Whether you develop cancer or not is not determined by your eating habit(s).
Should I use habit or habits?
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."
Comments
Another 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: