I have seen a large amount of explanation that explains how you get to the fat reserves with intermittent fasting and they all make sense. They explain that there is not one tank, but two tanks we work with. I understand insulin regulates the ability to tap into these reserves and infrequent eating helps.
What I can’t seem to understand or explain to others is: If it is not just calorie reduction that comes with a shorter eating window, where do those additional calories go?
Is it metabolically we simply burn them off with heat or other metabolic activities? Or does the presence of insulin put it right back into fat and the net loss we receive comes from the lower insulin during the fasting period as well as lowered intake?
Still not exactly sure what you’re asking about additional calories, but I’ll try my best to explain my understanding of it. The way I like to describe it is that controlling insulin with IF helps to direct a deficit to what we’re trying to do, reduce body fat.
Take for instance someone that maintains weight at 2,000 calories. They will maintain weight if those calories are spread out or in a smaller window. They will gain weight if they go up to 2,500 calories if those calories are spread out or in a smaller window. If they reduce calories to 1,500 they will lose some weight if those calories are spread out, but depending on the details of what they are eating, their body’s insulin resistance, etc their body might be forced to find another less desirable source like lean body mass or metabolically adapt to a deficit because insulin blocks fat usage. Where as that deficit is more freely able to fully be used from fat stores if that person ate 1,500 in a smaller window.
Granted human biochemistry and physiology is a lot more complex than that simple description, but hopefully that helps.
The theory also says there are potential gains beyond Calories In, Calories out based on the fast period. Your body will somewhat adjust energy expenditure up and down on a daily basis as needed to keep homeostasis, within reason of course.
Big benefit is the drop in insulin and corresponding potential over a longer term to drop insulin resistance based on insulin levels being regularly lower for more hours of the day. Lower average insulin => less insulin resistance => more weight loss/control.