Intermittent Fasting True Purpose

To any specialists out there, I would appreciate if you could clarify this for me. I know that the primary purpose (not all) is for burning fat / losing weight. But, is it meant to be done by simply making it easier for your body to be in a calorie deficit by essentially skipping the first meal of the day (16:8), or is it to put your body in a state of ketosis to help burn fat more efficiently (similar to keto diet)? In other words, if I fasted for 16 hours, and then proceeded to eat the rest of my normal meals for the day, I would obviously burn fat / lose weight because I’m in a deficit. But, let’s say I ate a lot more during those 8 hours and re-consumed those lost calories (same macros and everything) would there be any benefit at all from a fat burning standpoint, or would it be no different than a day where I just eat my normal diet? Thanks in advance.

Answer

You are asking whether IF mainly a) facilitates a reduction in intake; and/or b) causes an increase in expenditure. The literature thus far suggests that it’s mainly (a), with some studies also pointing at (b), on the order of a few hundred calories per day at best, with those individuals struggling with insulin resistance and its consequences being more likely to enjoy greater benefit. It’s important not to blow (b) out of proportion. Saying that, aided by IF, one may be able to afford an extra couple slices of bread per day, or lose weight slightly more easily if they so choose, is one thing; saying that they get to eat however much of anything they could possibly set their mind to, because IF grants them a ticket to mythical “fat-burning mode” where insulin is low and expenditure so high that energy balance practically becomes irrelevant, is something else entirely.