The Quality of the U.S. Diet Needs Improvement

According to a new Harvard study.

According to a new study from Harvard School of Public Health (HSPH) published Monday in JAMA Internal Medicine, the quality of the U.S. diet has actually improved in recent years due to, in large part, a reduced trans fat intake. But, the researchers say, the overall quality of the U.S diet still needs improvement.

“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, the study’s lead author and a doctoral student in the Department of Nutrition at HSPH.

Harvard researchers decided to investigate recent trends in dietary quality in the U.S. because of changes in the economy, nutrition policies, and food processing since the turn of the century. The researchers 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.” Wang says that evaluating these trends is important to help guide public health policy and improve strategies to prevent nutrition-related chronic diseases.

According to a report by HSPH:

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.

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.

The researchers noted that trans fat consumption has plummeted, and that “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.”

On another positive note, the study says that people are eating more whole fruit, whole grains, nuts, legumes, and polyunsaturated fats, which contributed to overall improvement in diet quality. People are also drinking fewer sugar-sweetened beverages. But, people are not eating more vegetables, nor are they eating less red and processed meats, and salt intake has increased, all of which the researchers found “disconcerting.”

The study also showed a significant gap in diet quality between people who are considered “rich” or “poor.” The results, unsurprisingly, showed that people with a higher socioeconomic status had a healthier diet than those with lower socioeconomic status. That gap in quality increased between 1999 and 2010.

According to the study:

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.