Is it going to explain 20 pounds of bodyfat? Absolutely not. But "calories in, calories out" isn't backed up by the science.
Now, you can get more specific than that and say "well this medical condition makes you more hungry" or "this medical condition means you can't get as much energy as you should from eating". But fundamentally, a condition like say PCOS isn't magic. It doesn't make you absorb food better, otherwise we would have already evolved to use that absorption process.
Having said all that: yes, no two people are exactly the same, we're not bunsen burners, etc. But the reason you're[1] fat is because you eat too much.
[1]: general you, not you specifically
While I don't know about the first half of this sentence (though I have my suspicions!) it's pretty obvious the second half is false. You're saying that we all have to process food identically because evolution has selected the optimal result in humans. But evolution does not product perfectly consistent results. In fact it relies on producing inconsistent results! Because sometimes small flaws turn out to actually be a benefit and get selected, that's how evolation works. So the fact that humans are a result of evolution does not prevent different people from having different abilities to absorb nutrients.
> But the reason you're[1] fat is because you eat too much.
You went to the trouble of mentioning CICO and then totally forgot about CO! Obviously you could extend this sentence to "... and/or you don't do enough exercise" but, similar to the previous point, there are likely to naturally be variation in calorie outputs. In fact "running hot" might seem like a weakness but could be a perfectly valid evolutionary strategy, presuming it gave some other benefit (like sharper mind or stronger body, better for obtaining more food). It's quite possible for both strategies to be baked into one set of genes, perhaps selected by activity in childhood.
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It's self evident that CICO is true. It's just completely worthless for providing any insight. Very much a thought-terminating cliché as originally described.
This is technically true but a but specious. Obviously you shouldn't eat as much as Michael Phelps if you don't train like Michael Phelps. But it's probably a lot more actionable for you to eat fewer calories than for you to start training like an Olympic athlete.
It's really not. As I said above, people are not identical. Yes, evolution doesn't produce perfectly consistent results. However, absorbing nutrients is the direct foundation for the only thing that matters in the process of evolution: reproduction. You can't reproduce if you die from lack of nutrients. Given how much of humanity's existence has been staving off starvation and famine, any improvements would be heavily selected for, and would quickly spread.
As an extreme example, if you could survive on an apple per day, the next famine that rolled around would leave you pretty free to repopulate with your superdigestive genes, since most everyone else would be dead.
> You went to the trouble of mentioning CICO and then totally forgot about CO!
I don't really understand the point you're trying to make in this paragraph. Even if some people "run hot" or they have some magic gut that lets them survive on an apple per day or whatever, it's still a fundamental truth that if they're fat, they're eating too much. Yes, someone can exercise more or whatever to change their output, but the reason they're currently fat is because they're currently eating too much.
> It's self evident that CICO is true. It's just completely worthless for providing any insight. Very much a thought-terminating cliché as originally described.
Yes, no, and no. As described above, there really are people that think "I eat just an apple a day and I can't lose weight!". CICO is a baseline for saying "no, that's impossible". It's not a thought-terminating cliché, it's making sure that everybody is on the same page of accepting basic science.
If that was true, shouldn't we have evolved to hibernate at some point?
> You can't reproduce if you die from lack of nutrients.
You also can't reproduce if you can't run fast when a wolf is hunting you. Those muscles are going to take some energy even while not running away from a wolf. I think you're trying to reduce evolution and reproduction to a single variable, which is a mistake.
I dunno, I think you might be surprised by how many people genuinely do not seem to understand it. It's valuable to them if they are willing to listen, problem is a lot of the time they really aren't, hence their problem.
This is itself a thought terminating cliche. Has anyone actually checked?
Within a pretty tight margin, calories in minus calories out DOES predict weight gain. The real question is why someone feels the need to eat more calories than they burn even when they already have ample stores of calories, and what they or others can do to change this. And THAT is a much more interesting question.
Thermic effect of food, for instance, seems to be the phenomenon where the metabolism increases after a meal. Metabolism is calories-out. So thermic effect of food isn't a refutation of CICO, just a complication. CICO is still the primary mechanism of weight control.
The main actual counterexample to CICO is water retention.
You are correct that water weight can cause spikes in weight measurement, but this is just a contributor to weight as a noisy measurement, not an example that it is not helpful.