For decades, the federal government conducted national dietary surveys in order to track Americans’ food and nutrient intake and where Americans get their food. However, technological differences in the methods of conducting these surveys made long-term analysis of trends difficult.

Federal dietary surveys conducted from 1977-2012 asked whether or not food was eaten at home and where the food was acquired. The food source coding changed over time, but for the most part the sources remained consistent, including: at-home food (supermarkets, small grocery stores, or other retailers) or food-away-from-home (F.A.F.H.). Subcategories of F.A.F.H. include full-service restaurants with wait staff, fast-food establishments without wait staff, school or day care meals, and a catchall “other” subcategory including vending machines and other miscellaneous sources. This consistency in the classification of food sources has allowed researchers to link the surveys and more accurately look at eating trends, according to a June 6 article on Amber Waves, an on-line publication of the Economic Research Service (E.R.S.) of the U.S. Department of Agriculture.

Researchers at the E.R.S. and the University of Georgia recoded the food sources of the dietary surveys between 1977 and 2012 to be consistent. By linking the surveys and providing consistent F.A.F.H. definitions, the researchers were able to consolidate the data and analyze the changing long-term trends of where consumers of different ages and income-levels acquire their foods. The results of the analysis may help improve targeting subpopulations that require greater nutrition education and policy focus.

The approximately 30-year period of analysis showed a consistent decline in home-prepared food. About 65% of calorie intake was consumed from at-home food in 2011-12, a decline from about 80% in 1977-78. From 1977-2006, the share of calories from F.A.F.H. rose to 33.8% from 17.8%. The share of calories from fast-food establishments also increased to 15.6% from 5.6%in that time. During the 2007-2010 recession, calories obtained from F.A.F.H. dipped briefly to 29.7%, with a parallel drop in fast-food establishments to 13.2%. The data show that the recession was a time when Americans economized by spending less on F.A.F.H. as a whole, preferring the cheaper at-home option rather than just shifting to lower cost F.A.F.H. options. By 2011-12, however, calorie intake from F.A.F.H. and fast-food sources rebounded to 34% and 15.8%, respectively, according to the report.

The researchers also were able to analyze the shifting data based on income levels. Across the entire time period, high income (above 185% of the federal poverty level) consumers received higher calorie intake from F.A.F.H. Both high and low income consumers still consistently increased F.A.F.H. consumption.

Across both income groups, fast-food was the leading source of F.A.F.H. calories throughout the time period. High income consumers had a larger share of calorie intake during a majority of that time period. But in 2009-2010, high income calorie intake from fast-food establishments dropped to about the same as low income consumers. In 2011-2012, low income calorie intake spiked to 16.4% from 15.3%, slightly higher than that of high income consumers.

The growing share of calorie intake from fast-food restaurants is paralleled among children (ages 2-19) compared to school food. In 1977-1978, children received less than 4% of daily calorie intake from fast-food sources. In the following years, children’s share of calorie intake from fast-food rose sharply. Intake peaked at 16.5% in 2003-2004 and fluctuated in the subsequent years, dipping to 12.6% in 2009-2010 and then rising again to 14.3% the next year.

In terms of income among children, low income children consistently ate more school foods than high income children, researchers found. This consistency may be attributed to a U.S.D.A. program allowing children in households with incomes at or below 185% to be eligible for either fully subsidized or reduced price school meals. Children in high income households received a greater share of calorie intake than children in low income households until becoming fairly even in 2009-2010.

The analysis of the data by researchers suggests Americans’ shifting preference toward F.A.F.H. This change is coupled with Americans’ growing preference of fast-food as a source of F.A.F.H. intake.