Sure, but wouldn’t the calorimeter’s reading still be the theoretical maximum since it’s based on thermodynamics? In other words, an inefficient metabolism may see a net gain of fewer calories, but it shouldn’t ever see greater.

I am a schmuck on the interwebs who went to school for microbiology and I can say for certain that the human body does not violate the 1st law of thermodynamics. Calorie deficit = your body must free up stored energy (in fat) to have enough energy to continue breathing = weight loss. Unless your body is able to create sustainable free energy out of a vacuum or unless you have a horrible genetic disorder that breaks down your bones for energy or unless you are dead

I’ve not used a calorimeter, but my understanding is that is just measures heat energy from burning things. Things like sucralose and aspertame likely WOULD read as caloric in that kind of measurement, because they contain chemical energy. The reason those sweeteners read as 0 in nutrition labels is because of how we metabolize food. Or in this case, how we don’t: we can’t digest sucralose and similar sweeteners. It goes in, your tongue says “yay!” and you poop it out.

Also a schmuck on interweb; but healthcare is my area of expertise, so I’ve got a handful of college level human anatomy & physiology, nutrition, and microbiology courses to draw from here. I was also a fatass who wanted to join the military back in the day, which required losing a lot of weight - decided to approach it as scientifically as possible (there’s a LOT of fad misinformation surrounding weightloss), and I can’t complain about the results.