Thanks for the comment! You’re of course right that the surest way to lose weight is for a person to consume much less food (or calories) than they did before. But I want to pick up on one thing you said:

“The calorie may be a flawed unit, it is still a measure of the maximum energy something may impart.”

The calorie (as far as nutritional labeling is concerned) is not meant to measure the maximum energy in food — it is intended to tell us the energy content available to our bodies. In fact, Atwater’s original values (calculated with the bomb calorimeter) were adjusted to account for our digestion as we understood it at the time. For example, we knew protein was digested less efficiently, so we reduced the number of calories assigned to a gram of protein.

The problem is that even with these adjustments, the calorie estimates are inaccurate. Even worse, the inaccuracies aren’t random but appear to be systematic: they are reasonably accurate for processed food but consistently overestimate the calories in whole food. So my central complaint is that if you use calories to compare one food against another, you may be misled. If you pick processed food B because it has less calories — guess what, not only could food B be less healthy, it might actually provide your body with more energy than food A.