&gt; I&#x27;m still pretty sure that calories-in&#x2F;calories-out theory is more-or-less correct.<p>Unless someone has overturned the laws of thermodynamics, it is correct. CICO rules over all, and it&#x27;s simple but not <i>easy</i> to lose weight, due as you put it to psychological factors.<p>As for the research about most people having the same metabolic rate, here&#x27;s a link: <a href="http:&#x2F;&#x2F;examine.com&#x2F;faq&#x2F;does-metabolism-vary-between-two-people&#x2F;" rel="nofollow">http:&#x2F;&#x2F;examine.com&#x2F;faq&#x2F;does-metabolism-vary-between-two-peop...</a><p>TL;DR - almost all people of the same height and weight will be within 200-300Kcal of each other BMR wise. There are some outliers, but not enough to cover all the people claiming to be special snowflakes. And even if someone does have a &quot;slow metabolism&quot;, that changes nothing: they still had to overeat to get fat. Mass doesn&#x27;t come from nowhere.