Eating out accounts for more than one-third (34 percent) of the daily calories consumed by Americans aged 2 or older, according to the USDA's Economic Research Service. That share was just 18 percent in the mid-1970s. Behind the rise of eating out (or what the USDA calls "food away from home") is the growing importance of fast food to the American diet. The fast-food share of daily caloric intake has nearly tripled in the past three decades...
Fast-food share of daily caloric intake
Fast food has become essential for busy workers and parents. Among lower income households in 2011-12, fast food provided 16.4 percent of daily calories. For higher-income households the fast-food share was 15.3 percent. Fast food accounts for a much larger share of children's daily caloric intake than school food. Children obtained 14.3 percent of their daily calories from fast food in 2011-12 (up from less than 4 percent in 1977-78) and about 7 percent from school food.
Source: USDA Economic Research Service, Linking Federal Food Intake Surveys Provides a More Accurate Look at Eating Out Trends