Olfaction and Nutrition

The most characteristic feature of animal life is that animals must actively seek and select their foods in their natural environment. A natural product is considered as a food of a particular species when it is currently selected and effectively eaten by members of the species and when, in addition, it corresponds to some of its nutritive requirements. Thus, to be a food, this natural product must possess two different series of biochemical properties. These properties act successively, as sources of information for the C.N.S., in the control system regulating food intake. In a first step, at the entry of the alimentary canal, the food is already controlled through its stimulating activity upon the various sensory systems level. As a result of this oral sensory appraisal, the food is either accepted or rejected and, when accepted, is eaten in definite amounts. This sensory activity to foods is a critical determinant of innate or acquired feeding responses, insuring an oral selection and a metering of intakes. Through the second step of action of foods in the feeding process, these orally determined responses to food are “regulated.” At the post-absorptive and systemic level, food as a nutrient acts as a metabolic signal upon regulatory centers and, through positive and negative feed-back mechanisms, “modulates” oral feeding responses.