Nutrition therapy is the science of treating disease and promoting health by the use of specific nutritional factors, together with the elimination of toxic and allergenic materials from the diet. Minerals, vitamins, essential fatty acids, amino acids and other supplements are prescribed in therapeutic doses for a medicinal effect. Nutrition therapists pay attention to the possibility of food allergies which may be diagnosed by fasting followed by the reintroduction of foods one by one. Less conventional methods are also sometimes employed, including sublingual tests and applied Kinesiology. Specialist laboratory services are sometimes used to analyse specimens of blood, urine, faeces or saliva.