Not sure if I am reading your response correctly, so would you agree or disagree that it is possible for two people to eat the same food, do the same work, and yet one of them will be thin and the other one will be fat, because of some combination of:

• different gut flora;
• different genes contributing to efficiency of digestion;
• different genes contributing to efficiency of keeping body temperature constant;
• (other stuff I forgot to mention).

In other words, that there is such a thing as "metabolic privilege", which is usually denied or ignored by the "calories in, calories out" proponents.