May 1 (HealthDay News) -- People with higher levels of education and income tend to eat healthier diets, but pay more for selecting foods that are less energy-dense (lower calorie/higher nutrient content), a U.S. study finds.

Less energy-dense diets are associated with lower rates of obesity, type 2 diabetes, cardiovascular disease and some forms of cancer. Improving diet quality by lowering energy density is standard advice for weight control, cancer prevention and better health, according to the University of Washington researchers.

Their study included 164 adults in the Seattle area who recorded their usual frequency of consumption of 152 foods and 22 beverages, along with portion sizes. They also provided four-day dietary records and completed demographic and behavioral questionnaires.

The researchers found that higher dietary energy density was associated with higher intakes of total fat and saturated fat and lower intakes of dietary fiber, potassium and vitamins A and C. Daily diet cost was $6.72 per day for men and $6.21 per day for women, which reflects the fact that the men ate more than the women. But women spent $8.12 for each 2,000 kcal of dietary energy, compared with $7.43 for men.

Diets with lower energy density and higher nutrient content were more costly than those with higher energy density and lower nutrient content. Higher quality diets were associated with higher household levels of education and income. Education was a more dominant factor than income.

"The findings that higher-quality diets were consumed by women of higher [socioeconomic status] and more costly per 2,000 kcal has implications for epidemiologic studies of diet and chronic disease," concluded study authors Pablo Monsivais and Adam Drewnowski.

"Nutritional epidemiology has historically been based on the premise that nutrient exposures are directly linked to health outcomes. However, nutritional status is also intimately linked to socioeconomic status, and the findings reported here raise the possibility that the higher monetary cost of nutritious diets may provide one explanation for these observations. Future studies, based on more representative samples, will be needed to elucidate the connections between diet quality and diet cost across socioeconomic strata," they wrote.

The study appears in the May issue of the Journal of the American Dietetic Association.

SOURCE: Journal of the American Dietetic Association, news release, May 1, 2009