We were taught (incorrectly) that wight loss was a simple formula of calories in and calories out. But it is way more complex. If you take an obese person with metabolic syndrome, and starve them, the body will eat their muscle first, and leave the fat behind. Additionally, when starved, the metabolism slows further, to the point where the body needs almost no calories, because it is burning no energy. Muscle is gone, there is nothing to burn the calories. Think of what happens to a bear in the winter when it quits eating (hibernation). Muscle is easier for the body to eat than fat, so it goes first. So there is a complex metabolic situation, that is not really well understood. It involves hormone balance, the type of energy delivered to the body, and the type of muscular activity that the body performs. Nowhere in that equation is there an emphasis on calories. Body builders may eat 6-10,000 calories a day, and their exercises may only burn1-2000 calories. So what happens? This area of medicine is super boring, very complex, and there are few studies and guidelines to help physicians treat their patients. You will find that area of expertise has largely moved out of allopathic medicine into cash based performance and wellness clinics that combine hormones with prescription meds, nutrition and exercise.