It depends on the approach taken to the topic; in previous cases, Diet quizzes have gone to food simply because of the subject matter of the quiz. While diets do affect health and well-being, they usually work separately, but in tandem with exercise and fitness. It's also a bit limiting to look at diets as 'restrictions', but I guess that's the way they're marketed.
My roommate is a personal trainer, so I've been getting earfuls.
Either way, in this case it's very, very likely Hobbies, but it would be very easy to swing it into a Nutrition quiz in Sci/Tech with the proper spin. Or Global Trivia. Or other options.
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