See also nutritional supplements
While much of the world's interest in nutrition is essentially avoiding starvation, that of developed countries is far more how to avoid the intersection between the normal urge to eat and the shareholders' desire for return on their investment from killing people.
Doctors tend to be asked very specific questions on nutrition, to which the most appropriate answer is a menu rather than a domestic science GCSE course.
Nutrition interacts with disease and treatment of disease in very complex ways. So the generality that Homo sapiens has evolved as an omnivore and needs a balanced diet of moderation for optimal lifespan and morbidity is very true, but you can also modify your diet to achieve specific goals. Such goals may be at the expense of harm in other spheres that are not apparent from first principles.