Outlined in this month’s issue of the Journal of Nutrition, the Nutrient-Rich Foods (NRF) Index proposes a new model for ranking foods based on their nutrient composition, which could be used to help consumers improve their diets.
The researchers, including Adam Drewnowski, PhD, director of the Center for Public Health Nutrition at the University of Washington, said the work was undertaken to “provide a positive, science-based approach to inform people about what to eat rather than what not to eat”.
They said the index comes in response to the call from the 2005 Dietary Guidelines for Americans Committee to develop “a scientifically valid definition of nutrient density to help with nutrition guidance”.
Balancing beneficial nutrients
The researches noted that a number of nutrient profile models already exist. However, they said that “if nutrient profiling is to remain a science, it needs to follow science-driven rules”, based on prevailing scientific knowledge and taking into account both the nutrients that should be limited in the diet as well as those that should be encouraged.
The NRF indices were validated against the Healthy Eating Index, which is a measure of diet quality recently updated by the US Department of Agriculture (available here).
The researchers evaluated different formulas including hundreds of varying numbers and combinations of nutrients in order to find a formula with the greatest correlation to the HEI.
The formula chosen as the NRF Index is based on 100 calories and takes the sum of the percent daily values of nine nutrients to encourage minus the sum of percent daily values of three nutrients to limit.
Nutrients to encourage were protein, calcium, magnesium, iron, fiber, potassium and vitamins A, C and E. Nutrients to limit were saturated fats, sodium and added sugars.
Diet scores based on a family of NRF indices were “significantly” related to HEI, wrote the researchers, adding that those algorithms that best predicted HEI included both nutrients to encourage and nutrients to limit.
“These results confirmed that better diets do not necessarily come from just restricting certain nutrients; the addition of beneficial nutrients is critical for a higher diet quality.”
The researchers said their indexing system was used to examine scores within defined food groups, and was able to distinguish nutritional benefits within these groups.
Further research is necessary to examine whether standardizing scores across food groups would allow the development of “even more useful tools” to help consumers select the most nutrient-dense choices from a food group and ultimately improve their diet.
“Other nutrient profiling efforts should also conduct validation analyses similar to those presented to ensure the approach used is related to an objective measure of diet quality,” they wrote.
“Considerable research is still necessary to determine how to best present nutrient profiling to consumers in a way that will actually lead to selection of foods that improve the overall diet.”
Development and Validation of the Nutrient-Rich Foods Index: A Tool to Measure Nutritional Quality of Foods
Journal of Nutrition 139:1-6, 2009
Authors: Victor L. Fulgoni III, Debra R. Keast, Adam Drewnowski