If losing fat were as easy as "calories in = calories out", then more people would do it. While it is strictly true, the problem is that you we don't understand the exact equations for both calories in and calories out, and we often don't have control over the parameters. What will you do about you gut flora, which can alter just how efficiently calories in concerts to calories out?

There are many and powerful issues at hand. You cannot just dismiss the issue as thermogenic.