Fast Food

Fast food doesn't make you fat, its the quantity of food you eat that makes you fat. And according to this post:

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 results for urban and suburban consumers were similar.

Fast food can only be blamed for increasing caloric intake at most 24 calories at day. Since 140 calories extra a day will increase your steady state weight by about 10 lbs, at most this means 1.5 lbs.

Time to look elsewhere for a scapegoat. How about the mirror?