WASHINGTON (AFP) - Americans are eating a bit less, dining out fewer times and consuming slightly healthier food, the United States Department of Agriculture (USDA) said in a study released on Thursday, calling the finding "encouraging". Between 2005 and 2010 the number of calories consumed each day decreased 5 per cent among working-age adults, the study reported.

Fat consumption also decreased, while fiber consumption increased, it added, based on a survey of nearly 10,000 adults.

Spending on food prepared outside the home - whether at restaurants, via to-go food or other means - decreased 13 per cent. Fast food accounted for roughly 40 per cent of prepared meals.

In 2010, Americans consumed around 30 per cent of their calories from meals prepared outside the home, compared with 35 per cent in 2005. And the number of meals eaten at home increased from 5.8 a week to 6.29.

These reductions "accounted for 20 per cent of the improvements in diet quality," the study said.

The number of meals from outside the home began to slowly climb in 2010, the study authors noted, but they said consumers were more mindful of the food's quality.

Overall, there were "encouraging findings" that "more Americans are paying attention on nutrition facts and prioritising nutrition in the household," said Mr Kevin Concannon, USDA under secretary for food, nutrition and consumer services.

More than one in three adults, or 78 million Americans, is obese.

The epidemic has resulted in an increase in public and private initiatives to combat Americans' overweight lifestyles, which are blamed for an estimated US$190 billion (S$242 billion) in medical spending each year.