Milk is considered as a food with a relatively high number of nutrients for the quantity of energy it provides, known as the nutrient density. What is nutrient density and how is this calculated?
Within the science of nutrition, attention is increasingly being paid to food patterns as opposed to focusing on the intake of individual nutrients. The thinking is that people do not consume individual nutrients, but eat a wide range of foods within food intake patterns. Various methods have been developed to assess the quality of these food patterns from a health perspective. The Nutrient Rich Food index (NRF) provides information about the nutrient density of foods and ranks food on the basis of their nutrient content. (1-2)
Foods in the main food groups provide proportionally more nutrients in relation to daily energy needs for health and maintenance of the body (3). Therefore the foods making up the main food groups are considered to be ‘nutrition-dense’. In contrast foods outside the main food groups, such as snacks, often have a high energy density but with fewer nutrients. With respect to nutrient density, foods are assessed for the quantity of nutrients per 100 g, 100 kcal or per serving (4). In the UK the nutrient profiling model was developed by the Food Standards Agency (FSA) as a tool to differentiate foods on the basis of their nutrient content per 100 g of a food or drink. Actually, this approach is considered to be most in line with achieving the Dietary Guidelines.
Determining nutrient density
It is not a simple process to determine the nutrient density of foods and provide an objective method for assessing nutritional quality. On the one hand, this is because there is not always sufficient consensus about the adequate intake of a nutrient and on the other hand it is hard to translate a nutrition-dense food pattern into health. The nutrient density of a food can be calculated with the help of the NRF index (Nutrient Rich Food index). It is determined if only the ‘positive nutrients’, such as protein, fibres, vitamins and minerals, are to be taken into account or if the quantity of added sugar, saturated fat and sodium is also included. This is called the NRF 9:3 calculation, in which protein, fibre, vitamins A, C and E, calcium, iron, magnesium and potassium are regarded as positive nutrients and added sugar, saturated fat and sodium as negative nutrients. For each nutrient the percentage of the Dietary Reference Intake achieved by consuming 100 kcal of the food concerned is assessed, with 100% being the cut-off point for the positive nutrients. For each food the percentage of the nine positive nutrients are totalled and then the percentage of the three negative nutrients are deducted. This leads to a range of foods with a high versus a low nutrient density. (4) Results of a prospective cohort study in the Netherlands show that a food pattern with a high score on the NRF 9:3 index is associated with a lower risk of mortality, but not with a lower risk of cardiovascular disease. Furthermore, this association was stronger for men than it was for women. (5)
Milk and other products
When a range of foods are assessed using the NRF (9:3) calculation, it becomes clear that vegetables, orange juice (pasteurised), fruit, low-fat yoghurt and skimmed milk, potatoes and meat (steak and pork chops) are products with proportionally higher amounts of nutrients per 100 kcal. Wholemeal pasta and bread have a high score as well. Chocolate, cake and biscuits are assessed as being low in nutrient density according to NRF (9:3). As each individual food has its own range of nutrients eating a varied diet remains an important consideration.
- Waijers P.M.C.M. et al. A critical review of predefined diet quality scores. British Journal of Nutrition, 2007, Vol. 97, p. 219-231.
- Drewnowski A. The Nutrient Rich Foods Index helps to identify healthy, affordable foods. Am J Clin Nutr 2010. 91: p. 1095S–1101S.
- Department of Health https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/216094/dh_123492.pdf. Accessed 23rd June 2017
- Drewnowski, A. (2010). The science behind the NRF index and its applications to food patterns. Presentation given at: Symposium on nutrient density 2010. Amsterdam May 21, 2010.
- Streppel, M.T., Sluik, D., Yperen, J. van, Geelen, A., Hofman, A., Franco, O.H., Witteman, J.C.M. and Feskens, E.J.M. (2014). Nutrient-rich foods, cardiovascular diseases and all-cause mortality: the Rotterdam study. European Journal of Clinical Nutrition, 2014, No. 68, pp. 741 – 747.