Nutrition does not produce useful questions. As others have said, both the questions and answers are usually vague and not definitive.
On the opposite side, it's a little silly to me that sports questions would be considered such a change in scope. Consider: "fitness" out of the context of sports is just a collection of exercise science, lifting and running. (We get the sport of bodybuilding, too, due to proximity to lifting.) The answers are repetitive because there's really not that much to say in so narrow a space.
In contrast, fitness in the context of sports creates all sorts of interesting questions about how to ideally train, avoid injury, and prepare for competition in a given sport. The interaction between science, fitness and sport seems to me to be more productive.
To me, having nutrition but not sports is as if Stack Overflow's scope included assembly code but no high-level languages. Sports (high-level/scripting languages) are the most common implementation of actual fitness (programming).
Fitness without sports is an antiseptic, health-only practice. Fitness + sports is exciting, engaging, social and deep.
Update - What was On-Topic When F&N was in Area 51?
The trend from the Area 51 on-topic/off-topic votes is crystal clear to me. I believe this is all the nutrition-related example questions:
- Whey was on-topic because it's fitness-related nutrition.
- Comparing Atkins, Zone & Paleo was off-topic because it's not related to exercise. (This one is borderline for me--if they connected it to their workout regimen I would allow it.)
- Nutrisystem was off-topic for the same reason.
- Calories-burned-during-kettlebells was fine because it's exercise-related.
- Figuring out the most nutritious vegetables was overwhelmingly voted off-topic.
- Dehydration was on-topic because it's a common athletic concern.
- Timing meals with workouts was on-topic because it's relevant for people who work out.
Nutrition as it relates to exercise is part of the scope. Nutrition on its own is not, and as far as I can tell, never has been.