Walter Willett

Study author Walter Willett

Quality of U.S. diet shows modest improvement, but overall remains poor

Trend from 1999-2010 also shows widening disparities in diet quality between rich and poor

For immediate release: September 1, 2014

Boston, MA ─ Dietary quality in the U.S. has improved steadily in recent years—spurred in large part by reduced trans fat intake—but overall dietary quality remains poor and disparities continue to widen among socioeconomic and racial/ethnic groups, according to a new study from Harvard School of Public Health (HSPH).

“The study provides the most direct evidence to date that the extensive efforts by many groups and individuals to improve U.S. dietary quality are having some payoff, but it also indicates that these efforts need to be expanded,” said Dong Wang, lead author of the study and a doctoral student in the Department of Nutrition at HSPH.

The study appears online September 1, 2014 in JAMA Internal Medicine.

Given changes in the economy, in policies related to nutrition, and in food processing since the turn of the century, the researchers decided to investigate recent trends in dietary quality in the U.S. They also investigated trends within different socioeconomic subgroups because differences in diet can contribute to variation in the burden of chronic diseases such as heart disease, diabetes, and cancer. Evaluating these trends is important to help guide public health policy and improve strategies to prevent nutrition-related chronic diseases, Wang said.

Data came from a nationally representative sample of 29,124 adults aged 20-85 from the U.S. 1999-2010 National Health and Nutrition Examination Surveys. The scientists evaluated dietary quality over time using the Alternate Healthy Eating Index 2010 (AHEI-2010), which rates dietary quality on a score of 0 to 110 (with higher scores indicating healthier diets), and which strongly predicts major chronic disease. They also used another dietary quality index, the Healthy Eating Index 2010.

Trans fat consumption plummets

The average AHEI-2010 score increased from 39.9 in 1999-2000 to 46.8 in 2009-2010, and the researchers found that more than half of the gain came from reduced consumption of trans fats. The overall improvement in dietary quality reflects changes in consumers’ food choices and in the makeup of processed foods, and is likely the result of public policy efforts and nutrition education, the authors said.

They noted that the significant reduction in trans fat consumption suggests that collective actions, such as legislation and taxation, are more effective in supporting people’s healthy choices than actions that depend solely on individual, voluntary behavior change.

Other changes in eating habits also played a significant role in boosting dietary quality. People are eating more whole fruit, whole grains, nuts, legumes, and polyunsaturated fats, and they’re drinking fewer sugar-sweetened beverages, the study found. On the other hand, people did not eat more vegetables or less red and/or processed meat. And their salt intake increased—which the researchers found “disconcerting.”

Gap grows between rich and poor

The results showed that people with higher socioeconomic status had healthier diets than people with lower socioeconomic status and that gap increased from 1999 to 2010.

These income-related differences in diet quality are likely associated with price (healthy foods generally cost more) and access (low-income people may have limited access to stores that sell healthy foods), the authors wrote. They also noted that education played a role: Dietary quality was lowest and improved more slowly among those who had had 12 years or less of school.

Among racial and ethnic groups, Mexican Americans had the best dietary quality, while non-Hispanic blacks had the poorest. The lower diet quality among non-Hispanic blacks was explained by lower income and education. The authors speculated that Mexican Americans’ better-quality diets may be due to dietary traditions or culture. Among all groups, women generally had better quality diets than men.

“The overall improvement in diet quality is encouraging, but the widening gap related to income and education presents a serious challenge to our society as a whole,” said Walter Willett, Fredrick John Stare Professor of Epidemiology and Nutrition, chair of the Department of Nutrition at HSPH, and senior author of the study.

Other HSPH authors included Yanping Li and Eric Ding, research scientists in the Department of Nutrition; Stephanie Chiuve, research associate in the Department of Nutrition; and Frank Hu, professor of nutrition and epidemiology.

Trends in Dietary Quality among Adults in the United States: 1999-2010,” Dong D. Wang, Cindy W. Leung, Yanping Li, Eric L. Ding, Stephanie E. Chiuve, Frank B. Hu, Walter C. Willett, JAMA Internal Medicine, September 1, 2014.

For more information:
Marge Dwyer
mhdwyer@hsph.harvard.edu
617-432-8416

photo: Kent Dayton

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Harvard School of Public Health brings together dedicated experts from many disciplines to educate new generations of global health leaders and produce powerful ideas that improve the lives and health of people everywhere. As a community of leading scientists, educators, and students, we work together to take innovative ideas from the laboratory to people’s lives—not only making scientific breakthroughs, but also working to change individual behaviors, public policies, and health care practices. Each year, more than 400 faculty members at HSPH teach 1,000-plus full-time students from around the world and train thousands more through online and executive education courses. Founded in 1913 as the Harvard-MIT School of Health Officers, the School is recognized as America’s oldest professional training program in public health.