A dietician is an expert in the field of food and nutrition. A dietician is like a physician for your diet.
People who study food in a scientific way are dieticians — they are experts on food and its effects. Dieticians study nutrition, which is the science that looks at what good and bad things various foods do to your body. If you need to change what you eat because of a health problem, like diabetes or obesity, you should consult a dietician. It’s also spelled dietitian.