"Can obesity be prevented by offering healthy food in canteens?"
This is not a good research question, why?
χ Closed question; the question can be answered with yes or no
χ Not specific; subject, period or field of research are not well indicated (What? When? Where?)
χ Not clear; the question can be explained in several ways
χ Not realistic; the more general the question, the more information you need to search and the more time you need.
"Over the past ten years, what has been the influence of the food supply in Dutch school canteens on obesity among higher education students?"
This is a good research question.
V The question is open, specific, and clearly defined.