&gt; I&#x27;m still pretty sure that calories-in&#x2F;calories-out theory is more-or-less correct.<p>From where do you derive this certainty?  There&#x27;s plenty of anecdotal evidence indicating significant variance among individuals.  Simply less efficient absorption of ingested calories would obviously make a huge difference, and I don&#x27;t think there&#x27;s any reason to think everyone absorbs calories with identical efficiency is there?