Yes, but there no reason to think that underweight and overweight people use the calorie information in the same way and in the same frequency.
If you just know that the average calorie consumption stays constant, you don't know whether some people changed their calorie consumption.
In 2006...75.7 million (in the U.S.) were overweight, 78.3 million were normal weight, and 3.9 million were underweight.
http://meps.ahrq.gov/data_files/publications/st247/stat247.pdf
I wasn't saying they use it in the same way. I was saying that the number of overweight people is so much greater than the number of underweight, that it would be incredibly unlikely for it to cancel.
Information that surprises you is interesting as it exposes where you have been miscalibrated, and allows you to correct for that.
I suspect the users of LessWrong have fairly similar beliefs, so it is probable that information that has surprised you would surprise others here, so it would be useful for them if you shared them.
Example: In a discussion with a friend recently I realised I had massively miscalibrated on the percentage of the UK population who shared my beliefs on certain subjects, in general the population was far more conservative than I had expected.
In retrospect I was assuming my own personal experience was more representative than it was, even when attempting to correct for that.