A person who advises others on dietary matters relating to health, well-being, and optimal nutrition; there is no legal definition, so education level can vary.
One who applies the science of nutrition to the promotion of health and control of disease, instructs auxiliary medical personnel, and participates in surveys.
A person who specialises in the study of nutrition and advises on diets.
A person who works in the area of nutrition for either animals or humans. A nutritionist in the field of human nutrition has usually had training that includes chemistry, biochemistry, human physiology and psychology, as well as food science and nutrition.