Panel 6.1 Daniel Wang and Walter Willett Harvard School of Public Health

Panel 6.1
Trends in Dietary Quality among Adults in the United States
Daniel Wang and Walter Willett
Harvard School of Public Health
Evaluation of population trends in dietary quality is essential because this provides feedback and
guidance for public policy. Since the late 1990s, many changes have occurred in the food supply,
national economy, and policy environment within the United States, and scientific evidence and
dietary recommendations have been continuously evolving, but the net effect on dietary quality
has not been clear. In addition, data on time trends in dietary quality among socioeconomic
subgroups are minimal; any differences could contribute to disparities in the burden of
noncommunicable diseases. We therefore used a nationally representative population of 29,124
adults aged 20–85 years from the US 1999–2010 National Health and Nutrition Examination
Surveys to investigate trends in dietary quality from 1999 to 2010, as well as trends within
socioeconomic status (SES) subgroups (1). Dietary quality was measured by the Alternate Healthy
Eating Index 2010 (AHEI-2010), an 11-dimension score (range, 0-10 for each component score and
0-110 for the total score) based on a combination of food and nutrient variables that have
established relationships with important health outcomes.
Over the 12 years, the mean AHEI-2010 increased from 39.9 to 46.8, suggesting a steady
improvement in dietary quality. This improvement reflected favorable changes in both consumers’
food choices and food processing motivated by both public policy and nutrition education.
Reduction of trans fat, from 4.6 grams per person per day in the late 1990s to 1.3 grams per
person per day by 2010, accounted for more than half of the improvement in dietary quality. This
large reduction could be largely attributed to public policy efforts. Because of strong scientific
evidence of adverse effects, since 2006 the US Food and Drug Administration (FDA) has required
that trans fat be included in nutrition labels. Also, many states and cities have taken legislative or
regulatory actions to limit trans fat use in restaurants and other locations. Most manufacturers
have reformulated products to reduce trans fat. Most recently, the FDA proposed an action to
eliminate trans fat from the food supply. Significant improvements were also found for other
components of AHEI-2010, including whole fruit, whole grains, sugar-sweetened beverages, nuts
and legumes, and polyunsaturated fatty acids, whereas sodium intake increased significantly over
time. Although improved modestly, the overall dietary quality remains far from optimal, and huge
room exists for further improvements, but only a small further gain can be made by reducing
intake of trans fats.
Dietary quality in the high-SES group was consistently higher than in the lower-SES groups, and
this gap widened over time from 3.9 points in 1999–2000 to 7.8 points in 2009–2010. Higher price
and limited access to healthy foods are among the possible explanations for the SES-related gaps.
Among different ethnic groups, Mexican Americans had a higher AHEI-2010 than non-Hispanic
white and black groups, possibly due to their dietary traditions and culture, whereas non-Hispanic
blacks had the lowest AHEI-2010 scores, which was largely explained by differences in income and
Our findings present challenges, including further developing scientific evidence to inform dietary
guidelines and additional strategies to address the SES-related disparities in dietary quality, for
both public health researchers and policymakers. Some experiences and lessons could be gained
from the process of trans fat elimination, which was a result of a combination of continuously
evolving scientific evidence, increasing consumer consciousness of harmful effects of trans fat,
regulatory actions, and reformulation of foods by manufacturers. In addition, this reduction
indicates that collective actions, such as legislation and taxation, for creating the environment
that fosters and supports individuals’ healthy choice are more effective and efficient to reduce
dietary risk factors than actions that solely depend on personal responsibility, such as consumers’
voluntary individual behavior change; populations with low SES are likely to benefit most from
the collective actions.
1. Wang DD, Leung CW, Li Y, Ding EL, Chiuve SE, Hu FB, Willett WC. 2014. Trends in
dietary quality among adults in the United States: 1999 through 2010. JAMA Internal
Medicine. doi: 10.1001/jamainternmed.2014.342.