[HumanOstrich]

Your body doesn't absorb all the calories you consume, nor does it expend or store as energy all the calories you absorb. Biology is complicated and CICO is a flawed and condescending oversimplification. It's like telling people "well, you know, if you eat more than you need to, you'll gain weight". Duh, not helpful.

[naming_the_user]

If you have a diet, say each week you eat X grams of meat, Y of vegetables, Z of cereals, and then next week (or for a number of weeks) you eat {X,Y,Z}1.1 or {X,Y,Z}0.9, that will have a net effect all else being equal.

There is nothing condescending about that. No-one is really claiming that all calories are equal e.g. you can replace 500 kcals of chicken with 450 kcals of olive oil and that be some sort of blockbuster great idea.

CICO does have an implicit "your diet isn't completely batshit insane" attached to it.

[s1artibartfast]

>It's like telling people "well, you know, if you eat more than you need to, you'll gain weight". Duh, not helpful.

It is a foundation to work from. Far better than believing that you can cheat thermodynamics, which is generally the alternative.

There are some fringe cases and nuances, but I have never heard of one that was relevant. Do you have a use case where deviations would matter?

Absorbed calories don't match label calories, but weight loss and gain are studied in terms of label calories, so it is irrelevant unless you are doing chemistry or particle physics.

Labels could be in terms of arbitrary moon units instead of calories and it would still be true. Weight loss is a function of moon units in and moon units out.