How do you know if your immune system is working?

Doctors are starting to promote eating healthy.  They're giving health advice they were not taught in medical school.  Chefs know how to cook foods.  They always use the best and freshest ingredients because it tastes good.  Doctors are now verifying that's also good for your health?  Do you need a doctor to tell us fresh ingredients are good for us?  We need real information that can fix your health problem.