[dragonwriter]

> It doesn't matter if they are exact for a given person so long as the labels are consistent. They are sufficiently consistent.

AFAIK, the main reasons that the calorie counts are not accurate for all people is variations in absorption for particular nutrients due to metabolic variations. These variations between people are specific to particular categories of nutrients (some are at the level of macronutrients -- particularly that I've heard of, differences in general fat or carbohydrate metabolism -- some more narrow.)

This would make the top-line calorie counts (or, more precisely, the relationship between top-line calorie counts of different products) inconsistent as well, in that for a person with absorption different than that targeted by the labeling, product A with 500 Cal and product B with 600 Cal might not merely provide different Calorie counts than 500/600 to that person, but product B might provide less Calories than product A, depending on the specific nutrient composition of those calories.