A nutritionist is a health specialist who devotes professional activity to food and nutritional science, preventive nutrition, diseases related to nutrient deficiencies, and the use of nutrient manipulation to enhance the clinical response to human diseases.

They may also advise people on dietary matters relating to health, well-being and optimal nutrition. Nutritionists have varying levels of education from someone with little or no education to an individual who has obtained a bachelor's, master's, or doctoral degree. This is because the term "nutritionist" is not a legally protected term in most parts of the world. As a result, the term "nutritionist" is subject to several interpretations. Many nutritionists appear on television, in newspapers and magazines, and write nutritional books, which may or may not have any real informational value regarding diet.

Nutritionists have a healthy regard for food and its life-sustaining properties. They are primarily concerned with the prevention and treatment of illnesses through proper dietary care. Nutritionists evaluate the diets of patients and clients suffering from medical disorders and suggest ways of fighting various health problems by modifying the patient’s intake of certain food items. As one nutritionist puts it, “It’s basically all about balance—the older you get, the more you begin to understand the importance of balance in your life, and your diet is no exception.”Hypertension, diabetes, and obesity are some of the common health problems that nutritionists work to alleviate. Through education and research, they also promote sensible eating habits in communities, schools, hospitals, prisons, clinics, and nursing homes. Like all other health professionals, nutritionists are motivated by a concern to improve people’s quality of life. Food manufacturers, advertisers,marketers, and some enlightened restaurateurs employ nutritionists to organize, develop, analyze, test, and prepare meals that are low in fat and cholesterol and virtually devoid of chemical additives. Nutritionists usually specialize in one of three major areas of practice: clinical, community, or administrative management. Clinical nutritionists service the needs of clients who are institutionalized. They develop, implement, and maintain nutritional programs for individuals in hospitals, nursing homes, retirement communities, day care centers, and prisons. Before proposing or implementing any dietary program, nutritionists must consult with doctors or other health professionals to ensure that medical and dietary needs are optimized. Community nutritionists are an integral part of health clinics, clubs, agencies, and HMOs. They advise individuals and groups on the nutritional practices that will promote good health. They also structure and recommend diet plans for whole families, often including guides to the correct preparation of meals and shopping for the right foods. Meal planning and preparation on a large scale, such as for a school district, requires the careful supervision of administrative or management nutritionists. Their responsibilities include preparing food budgets, purchasing food, ensuring that health and safety codes are strictly observed, maintaining records, and writing reports. Nutritionists often spend the greater part of their workday on their feet. Hot, steamy kitchens also figure prominently in a nutritionist’s career, although many of them end up working in well-lit, properly ventilated environments. But nutritionists must be prepared to work in environments that are not always equipped with modern conveniences or sometimes fall short of prescribed standards. In such work situations, the primary concern of the nutritionist will be to bring the work environment up to standard by enforcing health and safety codes and improving overall production capacity.