How healthy is the American diet? The Healthy Eating Index may help determine the answer, study suggests

23 Aug 2018 --- Nutrition experts have set out to determine if the 2015 update of the Healthy Eating Index (HEI), a measure of diet quality that is updated to reflect the Dietary Guidelines for Americans (DGA), can be used to determine the overall quality of the American diet adequately. The researchers found that this quality can also be defined, using the HEI, at different levels such as the national food supply, the community food environment and food intakes among population subgroups. 

“Tracking quality at these different levels is critical since we increasingly recognize the power of the food environment on eating behavior. That is, individuals cannot be expected to make healthy choices if those options are not readily available in the home, at work, at school and in the community,” says Jill Reedy, PhD, MPH, RD, Program Director at the Risk Factor Assessment Branch, National Cancer Institute, National Institutes of Health, and co-author of the papers in this issue.

The HEI is a measure of diet quality that can be used at various levels of the food stream. It has been applied by researchers to describe diet quality among population subgroups such as Mexican Americans, children and cancer survivors. It has also been used to evaluate the quality of food offerings across the food stream, including the US food supply, restaurant menus, grocery store circulars and US Federal food distribution programs.

Updates to the HEI and DGA
The HEI is updated every five years to reflect changes in the DGA. The most recent update was in 2015.

“The Dietary Guidelines for Americans evolve incrementally over time based on scientific evidence and updates to the HEI are designed to capture that evolution,” says Susan M. Krebs-Smith, Ph.D., MPH, Risk Factor Assessment Branch, National Cancer Institute, National Institutes of Health.

The 2015 edition has 13 components. Since the 2005 version, the HEI has been based on densities (e.g., amounts per 1,000 kcal), rather than absolute amounts and relies on a standard set of criteria that are applicable across individuals and settings, the researchers explain.

Notable differences compared to the previous edition are that saturated fat and added sugars are each separately tracked and excessive alcohol contribution to energy is not captured separately. The new version also incorporates modifications to the scoring procedures for legumes.

Testing sample menus with the newest HEI
The researchers set out to test the quality of the new HEI. Known high-quality sample menus from a variety of organizations such as the National Heart, Lung, and Blood Institute (DASH diet), US Department of Agriculture, Harvard Medical School (Healthy Eating Guide) and the American Heart Association were scored using the HEI standards. These menus all achieved high scores, ranging from 88 to 100 points.

At the next level of testing, data from the Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey were used to compare HEI-2015 scores across population subgroups to examine if meaningful differences could be detected.

The average HEI-2015 scores and ranges demonstrated reasonable variation across the subgroups examined, including groups differentiated by age, gender and smoking status. The results suggested that the index reflects the many dimensions of dietary guidance.

“These analyses demonstrated evidence supportive of validity and reliability for the HEI-2015, as has been shown in earlier work with the HEI-2005 and HEI-2010,” notes Dr. Reedy. “However, limitations in the HEI, as well as those inherent to dietary intake data more broadly, should be considered in any application of the index.”

The applications resulting from HEI scores are wide, the researchers explain: “The use of the most appropriate approach to calculating HEI scores for a given purpose can help build a stronger literature on the influence of dietary quality on health and disease risk, helping to inform future policies and programs to support health,” says Dr. Kirkpatrick, PhD, MHSc, RD, Associate Professor at the School of Public Health and Health Systems, University of Waterloo, Canada.

“The evidence base is stronger than ever before linking the 'total diet' – its dietary patterns, nutrient density and overall quality – to health promotion and disease prevention across the human lifespan. The work of these investigators will hopefully inspire other researchers and nutrition professionals to utilize the HEI-2015 broadly and establish other evidence-based innovations that fully embrace the 2015-2020 DGA's five cornerstone guidelines, and advance research and practice in clinical, public health and consumer settings,” concludes Dr. Millen.

Overall, as the range of food influencing the publics diet cannot always be guaranteed to be healthy, overarching models such as HEI can be used to detect where unhealthy diets are most prevalent and where the DGA are being followed the least, and perhaps even, why.