Nutrition researchers are called upon to inform policymakers of the consequences of consuming different amounts of various nutrients: how much is enough, how much is too much, and why. Traditionally, requirements were described by population-average levels and some measure of between-individual variation, whereas toxicities were described by single levels above which a toxic response was likely to occur. These statistics were used to estimate the prevalence of various adverse health effects in individual populations. Recently, accumulated data and improved understanding have led to more complete descriptions of the utilization of a few important nutrients and to the formulation of a model that includes both requirement and toxicity as extremes of the healthy-intake spectrum. This approach is based on estimating the full statistical distributions of individual nutritional deficits and surfeits within a population and using this to derive prevalence curves for specific adverse health effects. This information promises to provide policy planners with better tools to judge the health of populations, design feeding programs, and predict the sequelae of modifications in food supply and dietary habits. J. Nutr. 134: 1610S-1616S, 2004.