One thing that presumably massively influences calory-allocation may be the the prevalence of brown fat in some adult humans. I found a lot of unusual observations about my (privileged) metabolism suddenly explained by the presumed presence of it. See http://en.wikipedia.org/wiki/Brown_adipose_tissue#Presence_in_adults

There are some biases that make me favouring this explanation, and there is contradicting evidence, so I am not so sure anymore.