There is widespread scientific consensus that dining out increases the risk of eating excess calories and well-conducted studies confirm it. According to a comprehensive evaluation by USDA researchers, here is what you can expect in terms of extra calories when you choose to eat foods away from home.

• Each additional meal or snack consumed outside of the home comes with an average of 134 extra calories vs. the same meals or snacks prepared at home. (Keep in mind that if you did this just once a day with no increase in exercise, over the course of one year you would gain an additional 15 pounds!)
• For the average adult, eating out for lunch has the greatest impact, boosting daily calories by 158. Having dinner away from home adds an additional 144 calories; breakfast 74 calories; and snacks 100 calories.
• Overweight individuals are at the greatest risk of consuming extra calories when eating away from home. For a person with a body mass index (BMI) in the obese range (≥30), dining out adds an additional 239 daily calories.

(The Impact of Food Away from Home on Adult Diet Quality. ERR-90, USDA, Economic Research Service February 2010 and Food Policy, vol. 34(6))