Even though some restaurants provide you with a list of caloric value of their foods, it is most likely not true. Same goes for frozen foods.
Researchers found out that on average, 10 of the frozen meals had 8% more calories that the amount given on the label. Of course that doesn't seem too bad, unless you eat frozen meals regularly. Therefore, if you thought you were eating around 2,000 calories a day, but you were actually eating 8% more (that's 160 calories) because all your meals were prepared or frozen, then by the end of the week you would have consumed an extra 1,120 calories!!
Okay, so changes are you aren't eating that much frozen food, but let's talk about restaurants. Sadly, they are even worse. Restaurants underestimated the calories of their meals by an average of 18%! Therefore, you would be taking about 18% more calories than you realize, or 360 calories a day, 2,520 a week, or 131,040 calories a year, for an additional 37.44 lbs of fat. That's over a pound every 2 weeks!!
The good news: there is some regulation by the FDA.
The bad news: it only applies to packaged foods. And the FDA considers an "acceptable underestimation" of calories to be 20%. Restaurants don't have to follow any of these regulations, but frozen manufactures have to be within that 20% estimation range. Therefore, that 250- calorie meal could actually be 300 calories and still be within the regulation.
BOTTOM LINE - eat unprocessed, whole foods. They are better for you in general and have more of the good stuff (i.e. vitamins, minerals, fiber, etc.) and have less of the bad stuff (i.e. additives, sugar, etc.). They will still fill you up and nourish you better! And you know exactly what you are eating!