The 2005 Dietary Guidelines for Americans and U.S. Department of Agriculture's MyPyramid made a clear distinction between foods that were energy dense and those that were nutrient rich. Consumers were advised to seek out nutrient-rich foods (NRF) in preference to discretionary calories. However, the concept of nutrient density was not formally defined. The Nutrient Rich Foods (NRF) index is a formal metric of nutrient density that has been extensively compared with other methods and validated with respect to a healthy diet. The NRF index is based on 9 nutrients to encourage (protein; fiber; vitamins A, C, and E; calcium; iron; potassium; and magnesium) and 3 nutrients to limit (saturated fat, added sugar, and sodium). The NRF9.3 algorithm is the unweighted sum of percentage daily values (DVs) for 9 nutrients to encourage, minus the sum of percentage maximum recommended values (MRVs) for 3 nutrients to limit, calculated per reference amount and capped at 100% DV. The NRF index successfully ranks foods based on their nutritional value and can be applied to individual foods, meals, menus, and even the daily diet. Development of the NRF index followed scientific guidelines for nutrient profiling and was accompanied by extensive testing and validation.