Measures of diet quality
Currently, dietary patterns are gaining attention as people do not consume nutrients or single foods, but combinations of foods. Diet quality indexes have been developed to study optimal diets from a health perspective. To optimize diets in a broader sense, other aspects such as sustainability and affordability are now also being included.
Diet quality indexes
Nowadays, over 20 different indexes of diet quality exist. Most of these scores are derived from four extensively validated indexes, namely the Healthy Eating Index (HEI), the Diet Quality Index (DQI), the Healthy Diet Indicator (HDI) and the Mediterranean Diet Score (MDS). These indexes all take into account nutrients, as well as foods and /or food groups (annex 1).1
Another approach is the Nutrient Rich Food (NRF) index, which provides information about the nutrient density of foods and diets, rather than about the presence of specific foods or food groups. The most recent variant (NRF9.3) is based on nine beneficial nutrients (protein, fiber, vitamins and minerals) and three nutrients to limit (saturated fat, sugar and sodium).2
Diet quality scores and health outcomes
Most of the indexes mentioned above build on nutrient intake adequacy. Also, they are often associated with a modestly lower cardiovascular disease (CVD) risk and / or mortality. The predictive capacity of the various scores seems to be roughly in the same range, although the results cannot easily be compared across studies, as different reference groups have been used and adjustment for confounders varies.1 CVD-risk reductions of around 30% have been reported for the MDS and Alternative Healthy Eating Index (AHEI).3,4 A high NRF9.3 index score has been reported to be inversely associated with all-cause mortality, but not with CVD-incidence. Associations were stronger in women than in men.5
Beyond health: identifying the healthy affordable choice
Because achieving a healthy eating pattern is likely to be related to affordability of foods, scientists have linked the NRF9.3-index to (US) food prices, as illustrated in figure 1.2 This type of study helps identify those foods that have a favorable ratio between nutrient density and price.
Beyond health: identifying the healthy sustainable choice
Currently, the environmental impact of our diet is increasingly becoming a factor of importance. Therefore, nutrient density scores have been combined with Green House Gas (GHG)-emissions, creating the Nutrient Density to Climate Impact (NDCI)-index. This index can help identify foods with the most favorable ratio between nutrient density and climate impact (table 1).6
Table 1 Nutrient Density to Climate Impact (NDCI)-index for selected beverages
* Nutrient density = percentage of Nordic Nutrition Recommendations (NNR) in 100 g of product x number of nutrients ≥ 5 % of NNR/21.
** Greene House Gas (GHG)-emission in g CO2 equivalents per 100 g of product.
*** Nutrient Density to Climate Impact (NCDI)-index = nutrient density / GHG-emission.
Various studies based on diet modeling have shown that reducing diet-related greenhouse gas emissions, while ensuring nutritional adequacy, is theoretically feasible. Yet, it is important to realize that changes in dietary behavior should also be culturally acceptable, that the most nutrient-dense diets are not necessarily the most affordable and that sustainability metrics must go beyond mere carbon footprint. Population health and nutritional status should be central to the concept of sustainable nutrition security.7
Annex 1 Nutrients and foods / food groups in selected healthy diet indexes
|Fruit and vegetables||x||x||x||x|
|Mono- and disaccharides||x|
|Pulses nuts and seeds / legumes||x||x|
|Cereals / grains||x||x|
|Meat (and meat products)||x||x|
|Milk (and dairy products)||x||x|
- Waijers P.M.C.M. et al. A critical review of predefined diet quality scores. British Journal of Nutrition 2007. 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.
- Knoops K.T. et al. Mediterranean diet, lifestyle factors, and 10-year mortality in elderly European men and women: the HALE project. JAMA 2004. 292: p. 1433–1439.
- McCullough M.L. et al. Diet quality and major chronic disease risk in men and women: moving toward improved dietary guidance. Am J Clin Nutr 2002. 76: p. 1261–1271.
- Streppel M.T. et al. Nutrient-rich foods, cardiovascular diseases and all-cause mortality: the Rotterdam study. Eur J Clin Nutr 2014. doi: 10.1038/ejcn.2014.35. [Epub ahead of print].
- Smedman A. et al. Nutrient density of beverages in relation to climate impact. Food Nutr Res 2010. 54: 0.3402/fnr.v54i0.5170.
- Drenowski A. Healthy diets for a healthy planet. Am J Clin Nutr doi: 10.3945/ajcn.114.088542.