A study published in Public Health Nutrition shows that people who eat out may consume an average of about 200 calories more a day than when they cook at home.
The researchers examined the responses of 12,528 people aged 20–64 years who completed 24 hour dietary recall interviews for two days in the National Health and Nutrition Examination Survey (NHANES) 2003–2004, 2005–2006, 2007–2008, and 2009–2010. The survey respondents were asked about the source of each food and beverage item in terms of where it was obtained (e.g., from a store, fast food restaurant, full service restaurant, etc.).
The researchers found that people who ate at fast food restaurants or full service restaurants consumed an average of 194 and 205 extra calories per day, respectively. They also consumed more saturated fat (3 and 2.5 g extra, respectively) and salt (296 and 451 mg, respectively).
It should be noted that the study has limitations, such as the fact that the data was self-reported based on dietary recalls. In addition, physical activity and other factors that might affect food preferences and demand were not incorporated.