How does health, medical, and nutrition sciences realte to fitness, health, and wellness?

You need nutrients to survive. so basically your food that enters your body gets processed for energy by your small intestine. and the insulin from your liver gives your energy a key to go into your bloodstream to survive.

Those who are highly active.

They would need more calories, because they would need much more energy. While being active and eating less calories are important, you should be in moderation. People who are highly active, should be eating more to avoid becoming tired.