How your body regulates weight, fat storage and appetite goes way beyond gross energy balance.
https://www.medicalnewstoday.com/articles/320498.php
I normally find non-human obesity studies pretty boring, but this one is an exception. Researchers implanted rats and mice with weights equivalent to 15% of their body weight. Within a couple weeks they had lost an amount of body fat equivalent to the weight of the implants and returned to their pre-implant weight. Weight loss was solely the result of reduced food intake; the animals did not increase their physical activity. They got the same results using leptin-knockout mice, but not with mice deficient in osteocytes. Thus, our bones appear to have an osteocyte-dependent internal scale that regulates body fat storage and appetite independent of leptin. Pretty cool, and further evidence that the best way to not get fat is to sit on your ass as little as possible, but not simply because it
burns more calories.