All our calories are consumed by the metabolism. It’s like saying that all the wood fed to an oven is consumed by fire, it’s in the definition of the thing.

And, no, skipping meals doesn’t slow down the metabolism. What kind of survival strategy would that be, be hungry but don’t have energy to gather and hunt food? Up to about 48 hours of fast you get a metabolic boost on the order of 4 to 16%, then it returns to baseline before going down. And this isn’t fucking new and no I won’t cite anything because it’s been known since we can fucking measure it. If you find a source contradicting it it’s going to be some fad diet propaganda, not actual science. Searching online you’ll find papers and bad scans of graphs from the 70s but the data should go back at least to the 40s or so.

These mechanisms are practically identical in pretty much all living critters on earth as they’re very old because evolutionary speaking food insecurity is the rule, not the exception, meaning our genome is accustomed to it and our bodies right-out need periods of fast to switch on certain crucial programs, such as autophagy – which isn’t just starvation-grade “let’s eat all the muscle mass” but also “hey that skin is quite loose now let’s shrink it a bit”. General maintenance work, gotta rip out and recycle some old stuff once in a while to keep everything running smoothly.

And that’s before getting hunger and satiation hormones into play. “Just eat less calories” is kinda hard to do when you’re choosing the maximally difficult way to do it – compare and contrast the Minnesota starvation experiment. Sure all those diet comparisons generally show that equal reductions in calories imply roughly equal reductions in weight but have a look at which diets are ad-lib (eat as much as you want, but only certain stuff, or at certain times of day), or not (eat only so and so many calories), and how well people are able to actually keep those up.