Comment by JoshTriplett

> and (3) your metabolism slows down in response to, specifically, caloric restriction diets and your hunger rises which makes it difficult to estimate your calories out without indirect calorimetry.

This is the critical one that leads people to correctly argue CICO is largely useless for attempting to lose weight: the "CO" part of that is highly variable and is not merely a matter of being active. The body has all sorts of mechanisms that it can adjust to achieve the amount of storage vs burning that it wants to do, regardless of the amount of food consumed or the activity level.