The issue is: How are we defining calories IN?
Consider the extreme example of having a parasitic worm living in your digestive system. Is IN == [food passing mouth] or is IN == [food not being ingested by worm(s)]?
Now consider "normal" digestive flora. How are we defining IN here?
1. Having a hole in your gas tank (parasite(s) e.g. a tapeworm)
2. Having a modification to your fuel tank to convert ethanol into octane (non-parasitic digestive microorganisms a.k.a. "gut flora")
I was hinting at something bigger than just a nitpick. I'm hypothesizing that gut flora interfere with macronutrient ingestion in a statistically significant way.
Microorganisms exist which produce glucose from materials that, if ingested by a human, would be emitted as waste.
What if colonies of these microorganisms were present in the human gut and unevenly distributed in the population?
CICO is a great approach for the general population, and works great even amongst professionals that have weight management as their career (bodybuilders).