Did your studies include physics?
Yes. I studies physics and engineering during my career after graduating with a degree in Biology.
The vast majority of calories are burned through resting metabolism.
Eating less and exercising more more often than not reduces resting metabolism, such that what you would likely consider a ‘calorie deficit’ will just become a new metabolic equilibrium at the same body weight. It also triggers food cravings.
Two very good women friends of mine both eat far less than I do, and exercise far more than I do, but because they have a different endocrine system and have tried for years using calorie reduction, they are no longer achieving results.
Both of them could kick your ass too, but that’s a different story.