That's like saying "There are no secrets to space flight: For every action, there is an equal and opposite reaction. It doesn't matter if that involves Hydrogen, Hydrazine, or just big tubs of water -- throw them one way, and you'll move the opposite. Your choice of fuel doesn't change physics."

Of course fundamental physics laws hold. But some fuels and systems of using those fuels are more effective than others.

When it comes to diet, different foods and eating patterns do have different effects on our endocrine system, and that does affect how viably we can sustain ourselves on less calories. Different foods will also have different proportions that are retained vs passed the same day.

Unless you also capture ALL your own human waste, and measure it in a 'bomb calorimeter', counting calories (intake only) is not nearly as useful as you seem to think. If you disagree, drink 2000 calories of olive oil every day and eat nothing else, then come back after a year and tell me that calories are all that matter :) Disclaimer: Don't actually do that, because you would starve to death.