A dietitian, medical dietitian, or dietician is an expert in identifying and treating disease-related malnutrition and in conducting medical nutrition therapy, for example designing an enteral tube feeding regimen or mitigating the effects of cancer cachexia. Many dietitians work in hospitals and usually see specific patients where a nutritional assessment and intervention has been requested by a doctor or nurse, for example if a patient has lost their ability to swallow or requires artificial nutrition due to intestinal failure. Dietitians are regulated healthcare professionals licensed to assess, diagnose, and treat such problems. In the United Kingdom, dietitian is a 'protected title', meaning identifying yourself as a dietitian without appropriate education and registration is prohibited by law.

आहारविद्' या आहारिकीविद् (Dietitians) स्वास्थ्य से सम्बन्धित व्यवसायिक (प्रोफेसनल) है। वह भोजन की तैयारी एवं परोसने का निरीक्षण करता है, परिवर्तित आहार का विकास करता है, अनुसंधान करता है तथा लोगों एवं विभिन्न समूहों को स्वास्थ्यकर आहार की आदतों के बारे में शिक्षित करता है।