Nutritional disparities between America’s rich and poor are growing, despite efforts to provide higher-quality food to people who most need it. So says a large study just released from the Harvard School of Public Health that examined eating habits of 29,124 Americans over the past decade. Diet quality has improved among people of high socioeconomic status but deteriorated among those at the other end of the spectrum. The gap between the two groups doubled between 2000 and 2010. That will be costly for everyone.

The primary conclusion of the study is interesting, though, in that its focus is diet quality among the population as a whole. Without accounting for socioeconomic status, there has been, the study reads, “steady improvement.” People aren’t eating more vegetables, or less red or processed meat, and their salt intake increased—which the researchers call “disconcerting”—but Americans are eating more good things like whole fruit, whole grains, nuts, legumes, and polyunsaturated fats.

Frank Hu, a professor of nutrition and epidemiology at Harvard and one of the study’s authors, led with the good news when we spoke by phone.

“The good news is that the overall quality of the US diet has been increasing in the past decade,” he said. Hu likened the study to a nutrition report card, saying that “the grade is not that great, kind of in the B- range.” (“Not that great” might be more like a C- or D+ by non-Harvard-professor standards.)

The scale used, the Alternate Healthy Eating Index 2010, is the sum of 11 components, and it has been show to predict chronic disease, markers of inflammation, and death. Optimal diet quality on the index is 110, and right now we’re below 50.

Hu later called the growing gap between the rich and poor “disturbing.” That gulf is really the critical takeaway of this study. There can be no tenable “overall improvement” when there is growing disparity around a point so critical to preventive medicine, or when there is deterioration among any such sizable marginalized population.

Walter Willett, chair of the department of nutrition at Harvard School of Public Health, said in a press statement that the widening gap is related to income and education and “presents a serious challenge to our society as a whole.” Hu also drew a parallel between diet quality and income trends, noting, “After the financial crisis, the top one percent is doing very well—actually doing better, but the people in the low socioeconomic status groups are doing worse.”

Access to high-quality food is also important from a public health point of view because in low socioeconomic status groups, the burden of diet-related diseases is disproportionately high. “With deterioration in diet quality over time,” Hu said, “this may actually even increase disparities in obesity and other diet-related conditions.”

The research paper is not wanting for a politicized call to action. The authors write: “Collective actions, such as legislation and taxation, that aim toward creating an environment that fosters and supports individuals’ healthful choices are more effective at reducing dietary [disease] risk factors than actions that solely depend on personal responsibility.”

“We need to intensify efforts to educate the public about the role of diet in prevention of disease, and also implement policies that can help to improve the food environment,” Hu emphasized. Lack of affordable and accessible healthy foods among low socioeconomic status groups, especially in minority and inner city populations, he noted, has important implications for federal nutrition programs.

The US government has tried to address this disparity with the Supplemental Nutrition Assistance Program (SNAP), which receives almost $80 billion in federal funding annually. That is distributed among 47 million Americans who receive a monthly average of $133 per person. That money can be spent on any type of calorie, with no incentive to buy healthy food. Nutritionists tend to put “junk food” in quotes as an objection to things like Pixy Stix bearing the moniker “food” at all. (There are calories in paper, cotton, toenails, and Pepsi—should that qualify them as food?)

“SNAP can have a big influence with better incentives to purchase healthy foods like fruits, vegetables, and whole grains rather than soft drinks and highly processed quote-unquote junk food,” Hu said. “I think the programs should put more emphasis on quality of diet rather than just quantity. This is an area where the combination of nutrition education and financial incentives can really shape people’s attitudes and behaviors.”

One of the most dramatic changes in the food system is the reduction in trans fat consumption. Hu attributed the almost 80% reduction to policies requiring removal of trans fats from some food supplies and also putting trans fat measurements on food labels. “These kinds of policies have a very, very big influence on diet quality in populations,” he said.

The authors contend that one area where policy can play an even greater role is sugar-sweetened beverages (soda and juice). There has been a recent downward trend in sugary-beverage consumption, but as Hu said, “We still have a long way to go. Regulations such as taxation of sugary beverages and removing sugary beverages from vending machines in public schools, reducing accessibility of sugary beverages in public places—those kinds of policies can have a major influence on consumption.”

In accompanying commentary in the journal, Doctors Takehiro Sugiyama and Martin Shapiro of Tokyo’s National Center for Global Health and Medicine and UCLA’s Fielding School of Public Health, respectively, double down on the study’s unilateral call to action. Though they start out on a dubious foot, writing in the second sentence, “Excess caloric intake induces obesity and diabetes mellitus, which in turn causes cardiovascular disease”—technically true, but focusing on calories is out and focusing on food quality is in—they conclude with aplomb: “We urgently need to support multi-pronged initiatives to improve dietary quality for persons of lower socioeconomic status.”

This post originally appeared at The Atlantic. More from our sister site:

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