The evidence is there though.
A caloric deficit eventually forces the metabolism to slow down, hence the yo-to effect afterwards, whereas fasting doesn’t, not when implemented correctly.
In other words, yes you have the caloric deficit with fasting, but without some of the downsides of the body going into starvation mode.
If you are to believe the hyperinsulinemia theory of obesity, it actually makes perfect sense — it has been shown that insulin inhibits the body from accessing its own fat deposits. It has also been shown that you can make anybody fat by injections with insulin, no matter how thin they are. And there are several drugs known to make people fat by stimulating insulin. These are facts.
So by eating multiple meals per day, you’re stimulating your pancreas to trigger insulin in the bloodstream multiple times per day.
Thus the body will not have access to its fat store while that happens. As long as your insulin is high, no matter how much fat you have, you’re starving without eating food.
N.b. there has been plenty of evidence of this for the last several decades. What is new is the discovery of leptin and glucagon, two other hormones that are the opposite of insulin and that do a lot to fill in the blanks and explain why insulin is having the effects we’re seeing.
Also the metabolism is slowing down on caloric deficit, with the result that people eventually regain that weight back and then some, this has been shown in many studies, including that huge one from the Women’s Health Initiative.
When you’re doing keto or fasting, the insulin goes down. Again, this is a fact.
This allows the body to consume energy from its own fat deposits. This means that the metabolism shouldn’t slow down, when implemented correctly. Having fat isn’t for good looks, but an evolutionary advantage, we are supposed to use our fat store when in need, otherwise we would have evolved to excrete the excess.
Now of course, here we are talking of healthy people. It’s debatable if the metabolism slows down or not when we are speaking of diabetics or the obese. And actually I talked with people that claimed they measure their metabolic rate and it did slow down with fasting. So it works better for some people than for others.
But on the metabolic advantage, that advantage is undeniable for diabetics at least. In the next couple of years you will hear more and more of keto being promoted in the treatment of diabetes, because it works and there’s also a large study that’s still in progress, but that promises great results.
And btw, the reason for why keto hasn’t taken off in the medical community is due to perverse incentives. Nobody wants to invest hundreds of millions of dollars in proving that a diet works, because a diet doesn’t generate profit. The cold, harsh truth is that it’s more profitable to sell statins and synthetic insulin.
Funny enough, they did invest hundreds of millions (billions?) in trying to show that saturated fats and salt are bad, anything and everything to blame, except for sugar. All such studies failed of course, but that didn’t stop the dogma, anything to keep us consuming sugar, which is where the “_a calorie is a calorie_” bullshit comes from.