A method used in establishing nutrient needs, when biochemical markers of nutritional (nutrient) status are not available and/or there are no good intake-status relationships. It involves adding up the various factors that determine the requirement for maintenance of a defined plasma level or body store, and that is associated with the absence of adverse health effects, respectively normal tissue or body function. This requires measuring of the amounts of nutrients that leave the body via the faeces, urine and skin, either unchanged or as metabolites and also estimating the amounts that are required for growth, pregnancy or lactation.