A nutritional therapist seeks to work with a patient or client to improve or restore physiological and biochemical function in chronic illnesses through dietary guidance related to the individual's needs.

A clinical audit on 300 NHS patients treated by a nutritional therapist between 1990-1993 found the following percentages of patients reported a "definite, lasting improvement":

Headaches or migraine - 85%

Digestive problems - 82%

Hormone-related problems - 70%

Chronic tiredness - 55%

Skin diseases - 54%