Great opinion article from the New York Times on the inaccuracy of the calorie counts on nutrition labels. The author took 5 items and compared calorie count listed on the labels with the true calorie count from an actual calorimetry measurement. Turns out it can range anywhere from being spot on (Subway sandwich) to almost double the amount listed (tofu sandwich). Of course there will always be some degree of variation when foods are made and no label can be exact, the fact that they almost all underestimate the total amount is a little deceiving.
The author acknowledges that this is not a conclusive study, and he only measured one sample of each food, but it really gives you something to think about.
Despite the fact that we know the whole calories in vs calories out way of thinking is extremely incomplete, and doesn’t take into the account the types of calories as well as the subsequent hormonal responses elicited, calories still do matter.
So even if you try really hard to track everything you eat, you probably still need to program in an additional 10-30% margin of error. So if you calculate your daily consumption to be 2000 calories, if your goal is to lose weight, you should probably estimate that your actual caloric intake to be in the range of 2200-2600 calories.
This probably means the macronutrient numbers are also way off…