The quality of the U.S. diet showed some modest improvement in the last decade in large measure because of a reduction in the consumption of unhealthy trans fats, but the gap in overall diet quality widened between the rich and the poor, according to a study published in JAMA Internal Medicine.

An unhealthy diet is closely linked to cardiovascular disease, diabetes and some cancers. Eating a healthy diet is an important part of the strategy to prevent adverse health outcomes. Evaluating population trends in diet quality is important because it can offer guidance for public health policy.

Author Dong D. Wang, MD, MSc., of the Harvard School of Public Health, Boston, and colleagues used the Alternate Healthy Eating Index 2010 (AHEI-2010) to investigate trends in diet quality in the U.S. adult population from 1999 to 2010 using a sample of 29,124 adults from the National Health and Nutrition Examination Survey (NHANES). A higher AHEI-2010 score indicated a more healthful diet. The index’s components were scored from 0 to 10.

For fruits, vegetables, whole grains, nuts and legumes, long-chain omega-3 fats and polyunsaturated fatty acids (PUFAs), a higher score corresponded to higher intake. For trans fat, sugar-sweetened beverages and fruit juices, red and/or processed meat and sodium, a higher score corresponded to lower intake. The authors used a recently updated index, the Healthy Eating Index 2010 (HEI-2010) for further analysis.

The energy-adjusted average AHEI-2010 score increased from 39.9 in 1999- 2000 to 46.8 in 2009- 2010. Reduced trans fat intake accounted for more than half of this improvement. Scores increased by 0.9 points for sugar-sweetened beverages and fruit juice reflecting decreased consumption. Score increases of 0.7 points for whole fruit, 0.5 points for whole grains, 0.5 points for PUFAs and 0.4 points for nuts and legumes reflected increased consumption. A decrease in scores for sodium reflected greater consumption. Having a lower body mass index (BMI) also was associated with dietary improvement. Diet quality scores in the high-socioeconomic status (SES) group, associated with both income and education, were consistently higher than in the lower-SES groups and that gap widened over time from 3.9 points in 1999-2000 to 7.8 points in 2009-2010.

Researchers wrote: “Our study suggests that the overall dietary quality of the U.S. population steadily improved from 1999 through 2010. This improvement reflected favorable changes in both consumers’ food choices and food processing, especially the reduction of trans fat intake, that were likely motivated by both public policy and nutrition education. However, overall dietary quality remains poor, indicating room for improvement and presenting challenges for both public health researchers and policy makers. Furthermore, substantial differences in dietary quality were seen across levels of SES, and the gap between those with the highest and lowest levels increased over time.”