The percentage of Americans regarded as "food insecure" - lacking access to enough food for a healthy life - has edged down in the past few years but still represents over 17 million households, the U.S. Agriculture Department said on Wednesday.

About 14.3 percent of households were termed food insecure in 2013, down from 14.9 percent in 2011.

Rates of food insecurity were substantially higher than the national average in households with incomes near or below the poverty line, those headed by single women or single men, and those headed by blacks and Hispanics, USDA's Economic Research Service (ERS) said in an annual report.

Food insecurity was also more common in large cities and rural areas than in suburban and exurban areas. Exurban areas are communities further out from cities than suburbs.

Although the prevalence of sporadic food insecurity has fallen, the number of households with very low food security is persistent, USDA said, even as the U.S. economy has moved on from a severe recession that ended in 2009.

"Given improvements in employment and other economic indicators, some have wondered why food security has been slow to improve," said Alisha Coleman-Jensen, a social science analyst with the ERS's Food Assistance Branch and one of the authors of the study.

A separate ERS study found that although unemployment fell in 2012 and 2013, inflation and the price of food relative to other goods and services continued to rise.

Some 5.6 percent, or 6.8 million households, had very low food security in 2013, meaning that the food intake of some household members was reduced and normal eating patterns were disrupted at times due to limited resources.

USDA said that although households with children have higher food insecurity rates than those without children, kids are usually shielded from the disrupted eating patterns and reduced food intake that characterize very low food security.

Of the roughly 20 percent of households with children termed food insecure in 2013, only adults were food insecure in about half.

"Most parents try to protect their children from food insecurity to the extent they can," said Coleman-Jensen.

In some 360,000 households, parents reported that kids at times went hungry, skipped a meal, or did not eat for a whole day because there was not enough money for food.

Among states, the rates of very low food security in 2013 ranged from 3.1 percent in North Dakota to 8.4 percent in Arkansas.

Almost two-thirds of food-insecure households surveyed by USDA reported that in the previous month they had participated in federal food and nutrition programs such as the Supplemental Nutrition Assistance Program (SNAP), commonly known as food stamps.

About 46.2 million Americans - many of them children or the elderly - are currently enrolled in SNAP, down slightly from a peak of almost 47.8 million, in December 2012.