Other forms: dietitians
A healthcare worker who's an expert on food and nutrition is a dietitian. In hospitals, it's a dietitian's job to develop healthful menus for patients.
A dietitian's education includes learning in detail about the specific ways diet and nutrients affect human bodies. School districts, nursing homes, and hospitals all hire dietitians to plan balanced meals. In the case of a school, that might involve creative ways of making vegetables taste great. Anyone who's concerned about their diet can consult a dietitian for advice.