[steveplace]

Weight Change = CI - CO

Where CO has a CI input.

This has been known for while. Protein has a thermic effect which can change your CO.

But the equation still works.

[beagle3]

On the useless tautological sense. If you can't measure CO to within 20%, can hardly measure CI to within that range - then for all practical purposes, the equation does not work.

You may want to read about (lack of) precision in Atwater factors, to the tune of 50%, if you believe CI is easy to compute.