Problems are encountered in nutrition research designed to establish nutrient requirements. A nutrient requirement must be defined in terms of a specific criterion of response for animals of a given age, weight, sex and body composition. The experimental diet employed must be carefully defined in terms of protein source and level, energy source and level and a multitude of biological availability factors, both negative (e.g., phytate and fiber) and positive (e.g., anabolic bioactivity). Also precursor materials may contribute nutrient bioactivity to the diet. Having considered these factors, the data obtained must be subjected to appropriate statistical methods that will allow objective rather than subjective estimation of the maxima or minima being sought (i.e., the "requirement").
