If you are very careful about how you define “in” and “out”, to the point where it is nearly circular, and are concerned only about weight, not health, yes. It is still problematic in a number of ways, e.g.: if you just attack thr calories in side and have a relatively sedentary lifestyle, you will disproportionately lose lean body mass rather than fat, this not only is less than ideal as an end outcome, it also makes further weight loss more difficult because it reduces resting metabolic rate (and, therefore, minimum calories out) and makes it harder to do additional exercise to increase calories out.
It is likewis known empirically that, as actionable advice, its not particularly useful on its own besides those problems, for the same reason “don’t write bugs” is as advice on how to create correct software. Most serious weightoss advice incorporates CICO, but also adds layers on top dealing with the pragmatics of how to acheive that in a maintainable way (and usually also has at least some thought in how to do it in a way dealing with problems of naive CICO like those discussed above.)
> Is this really true and known empirically?
If you are very careful about how you define “in” and “out”, to the point where it is nearly circular, and are concerned only about weight, not health, yes. It is still problematic in a number of ways, e.g.: if you just attack thr calories in side and have a relatively sedentary lifestyle, you will disproportionately lose lean body mass rather than fat, this not only is less than ideal as an end outcome, it also makes further weight loss more difficult because it reduces resting metabolic rate (and, therefore, minimum calories out) and makes it harder to do additional exercise to increase calories out.
It is likewis known empirically that, as actionable advice, its not particularly useful on its own besides those problems, for the same reason “don’t write bugs” is as advice on how to create correct software. Most serious weightoss advice incorporates CICO, but also adds layers on top dealing with the pragmatics of how to acheive that in a maintainable way (and usually also has at least some thought in how to do it in a way dealing with problems of naive CICO like those discussed above.)