The report from the Centers for Disease Control and Prevention was based on data pulled from the National Health and Nutrition Examination Survey (NHANES), CBS News reported.
Fast food is a quick alternative to making a meal at home, and it's steadily becoming am increasing part of the American diet, the report noted.
However, the 2007 to 2010 fast food-calorie statistics are lower than the levels reported from 2003 to 2006, when the American diet was about 13 percent fast food, it said.
Researchers cited that eating fast food frequently has been linked to weight gain.
The CDC report revealed that more than one-third of U.S. adults are obese and that obese people had the highest percentage of fast food making up their diet.
Non-Hispanic black adults ate more fast food in their diet than non-Hispanic whites and Hispanic adults. Non-Hispanic blacks have the highest rates of obesity at 49.5 percent, according to the CDC.
Earlier research has linked obesity to many health conditions, including heart disease, stroke, type 2 diabetes and certain types of cancer.