Even in a car engine having different kinds of fuels changes how much of it gets converted to energy.
Your body is infitely more complex than a car.
Calories in calories out is not an immutable law.
If that were the case, you could binge eat 30,000 calories and then you'd somehow add 28,000 calories worth of fat to your body in one day, which just isnt how that works.
It actually can be, if you define both "in" and "out" in a way which makes it so; but for any definition of those terms where it is an immutable law, we, in practice, have only very rough proxy measures for at least one, and maybe both, of "calories in" or "calories out", and the problem then becomes mistaking the proxy for the actual figure of merit.
But the bigger problem is that CICO is only a starting point, it a set of targets, and an actionable plan that works in the real world isn't just the targets the plan is directed at.
Yes, it's complicated and there's subtleties; but CICO is the main truth of dieting, and trying to downplay its primacy is misguided or deceptive.
Did you bother to google before replying? Obviously not.
Why do you (and the other guy above you) feel the need to argue even when some topic is completely outside your expertise? Why not open your mind to a new idea and learn something?
> but CICO is the main truth of dieting
It's certainly what most physicians and most >25 BMI people believe. And how's that working out? (Think about it before you hit the trigger finger: how. is. CICO. working. out?)
Fine!