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U.S. Diet Quality Improves, But Still Not Healthy

Complex carbohydrates (Agricultural Research Service/USDA)

(Agricultural Research Service/USDA)

2 September 2014. A study by researchers at Harvard University shows some improvement in the health benefits of food eaten by Americans over the last decade, but the overall quality of the American diet remains poor. The study led by nutrition and epidemiology professor Walter Willett appears online in the journal JAMA Internal Medicine (paid subscription required).

Willett and colleagues — from Harvard’s School of Public Health, Brigham and Women’s Hospital, and University of California in San Francisco — looked for any changes in the quality of food eaten in the U.S. over the period 1999 to 2010, given the link between diet and various chronic diseases. That period experienced significant changes in the economy and several policy changes related to nutrition. The researchers also examined differences in diet among various ethnic and socioeconomic groups.

The team took a sample of more than 29,000 adult responses from the National Health and Nutrition Examination Surveys conducted from 1999 to 2010, which include items on diet and nutrition. The researchers then rated the responses on two dietary quality indexes: Health Eating Index 2010 and Alternate Healthy Eating Index 2010, which correlates with incidences of major chronic diseases.

The research team found the Alternate Healthy Eating Index score, which ranges from 0 to 110, increased overall from 39.9 in 1999-2000 to 46.8 in 2009-2010. More than half of the quality gain is from lower intake of food with trans fat, unsaturated fat artificially laden with hydrogen to remain solid, but that also adds LDL (bad) cholesterol and reduces HDL (good) cholesterol, increasing the risk of heart disease. The authors attribute the reduction in trans fat in diets to changes in food choices, including fewer processed foods.

The researchers also found Americans eating more whole fruit, whole grains, nuts, and polyunsaturated fats, and drinking fewer sugary drinks. At the same time, Americans were still eating about the same amount of red and processed meat, with no increase in the consumption of fresh vegetables. In addition, the team found an increase in the amount of salt consumed in diets.

People in higher socioeconomic groups had higher quality diets than people at the lower end of the socioeconomic scale throughout the study period, with the gap increasing during the decade. The authors attribute the gap to higher prices for fresh food and more access to sources of fresh food in high-income neighborhoods. The researchers also found education to play a role, with lower-quality diets and less improvement in diet quality among people with 12 years of schooling or less.

“The overall improvement in diet quality is encouraging,” says Willett in a university statement, “but the widening gap related to income and education presents a serious challenge to our society as a whole.” Many of the improvements, note the authors, were helped by policy changes, such as new laws in some jurisdictions banning trans fat, which influenced individual food choices.

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