WASHINGTON – Decades after the federal government first issued the Dietary Guidelines for Americans in 1980, the eating habits of most Americans neither match the government recommendations nor are moving significantly closer to the guidance over time, according to research conducted by the Economic Research Service of the U.S. Department of Agriculture.

In the study, “Americans’ food choices at home and away: how do they compare with recommendations?,” the E.R.S. researchers found a significant disparity between what Americans should eat and what they do for virtually every one of 23 broad food categories tracked.

Contributors to the report included E.R.S. nutrition experts and economists Joanne Guthrie, Biing-Hwan, Lin Abigail Okrent and Richard Volpe.

In their study, E.R.S. researchers compared grocery store purchases in 1998-2006 with food plan recommendations from the U.S.D.A. The food plans vary based on income levels — thrifty, low cost, moderate cost and liberal. The plans identify nutritionally appropriate shares or percentages of a household’s total food expenditures for the 23 categories of food typically bought by consumers. The researchers used Nielsen Homescan panelist data to estimate supermarket purchases.

“Panelists underspent on all categories of vegetables except potatoes,” the researchers said. “For example, they spent only 0.5% of their food budgets on dark green vegetables, while the food plan recommended 7%. Panelists also underspent on whole grains, whole fruit, lower fat dairy, nuts, poultry, and fish. Panelists overspent on other foods such as refined grains, fruit juices, regular dairy products (including whole milk and butter), and meats. Refined grains — which include non-whole grain crackers, cookies, breads, and pasta — accounted for 17% of the panelists’ spending instead of the 5% recommended in the U.S.D.A. food plan. Dietary guidance suggests limiting added fats and sugars, and U.S.D.A. food plan expenditure levels are correspondingly low, but the Homescan panelists’ expenditures for these categories were well above recommendations. Spending on convenience options, such as frozen or refrigerated entrees, was also higher than recommended.”

Of the 23 categories tracked, potatoes were the only one for which spending nearly matched up with recommendations — 2% of expenditures versus 2.1% recommended.

While eating out in general and at quick-service restaurants in particular often is fingered as a major contributor to rising obesity rates and nutrition related health problems, the E.R.S. said the role of what people eat at home should not be overlooked.

“Americans still obtain about two-thirds of their daily calories from food prepared at home,” the study said.

Offering additional perspective on their findings, the researchers noted that the problem of unhealthy food choices was not limited to certain ethnic groups or a particular socioeconomic class.

“Scores indicate that dietary quality is a general problem in the U.S. and is not confined to a particular economic or demographic group,” the researchers said. “Differences in household scores across racial groups, regions of the country, and income groups are relatively small, and all groups are in need of improvement. For example, scores rose slightly with household income, and at the extreme ends of the income distribution (annual incomes below $12,000 and above $200,000), average scores differed by 18%. Nevertheless, both groups’ scores indicated food purchasing patterns that were far from ideal when compared with recommendations.”

Additionally, the data did not show improvement over time in how consumers eat at home, with the sole exception of an increase in whole grains intake and a corresponding decrease in spending on refined grains. Still, even at the end of the research study period, consumers were spending far less than half of their grains expenditures on whole grains. Spending on fruits and vegetables declined over the study period while spending on packaged and processed foods increased.

Acknowledging “considerable room for improvement” in dietary habits, the researchers latched on to the good news in the report as holding the potential for making more generalized progress.

“Supply and demand both play a role in influencing consumer food choices, as illustrated by the recent trend toward increased availability and purchases of whole grains,” the study said. “Increased emphasis on the health benefits of whole grains likely caught the attention of both the food industry and consumers. This growing interest in whole grains led food companies to expand supply by offering a wider range of whole grain products, and consumers, in turn, increased purchases. Further success in changing dietary habits may depend on increasing consumer demand for healthful foods and the ability of industry to find products with improved health characteristics that also meet consumer preferences for convenience and taste.

“Affordability is another key consideration. The perceived high cost of healthy foods is often cited by consumers as a deterrent to purchasing them, yet recent E.R.S. research found that healthy foods like fruits and vegetables can cost less per portion than less healthy foods. Nevertheless, consumers may need to shift purchases away from foods for which they are overspending relative to the U.S.D.A. food plans to free up funds for purchases of healthful, under-consumed foods.

“Despite the benefits to overall diet quality, it can be difficult to convince consumers to change food preferences.”

While nutrition labeling has been mandatory for nearly 20 years, the researchers said use of the nutrition labels declined over the time period covered in the study.

“New government and private industry initiatives are striving to make food labels and point-of-purchase information more relevant to consumer interests, readily comprehensible, and motivating,” the researchers said. “The U.S. Food and Drug Administration, which regulates nutrition labeling of foods, has announced its intention to propose changes to existing practices.”

Shelf tags and front-of-package labels to help consumers identify more healthful food also may be helpful, they said.

In their analysis of away-from-home eating, the researchers said progress over the last 35 years has been even poorer than eating at home.