dietitian; nutritionist
A professional who plans and manages meals and nutrition, often in hospitals, schools, or care facilities. In Japan, 栄養士 is a national qualification distinct from 管理栄養士 (registered dietitian).
A dietitian manages the patients' meals at the hospital.
彼女は栄養士の資格を取るために勉強中だ。
She is studying to get a nutritionist qualification.