Depends on the country. In my country you either study sports science and then ad sports nutrition as a focus or you take a 3 year education as a diet assistant (basically a nutritionist) with an official government controlled curriculum.
You will learn about necessary biology, chemistry, physiology, nutrition, preparing food and then also can specialize further. A diet assistant is an interesting combination as they also learn to prepare everything.
A diet assistent will start with a salary of a little over 40 000$ / year so its not that bad.
The term nutrition expert etc is not protected. Everyone with a weekend seminar can use that term. Thats why you have so many of them. They grow like fungus

Especially with bodybuilding