Matsa and Anderson next looked at data on individual eating habits from
a survey conducted between 1994 and 1996. When eating out, people
reported consuming about 35 percent more calories on average than when
they ate at home. But importantly, respondents reduced their caloric
intake at home on days they ate out (that’s not to say that people were
watching their weight, since respondents who reported consuming more at
home also tended to eat more when going out). Overall, eating out
increased daily caloric intake by only 24 calories.
The researchers also find that greater access to fast food restaurants, as created by new highway construction, doesn’t much matter for weight. Here is more, including a link to the original paper.