I'm underweight. If there are a bunch of people like me
There are not nearly as many people like you compared to those who are overweight, or even those who are overweight and on a diet.
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.
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.