That's what was believed (back when doctors were searching for reasons for obesity besides CI>CO), but it was proven not to be true.  They have lower skin temp but higher core temps and higher hand temperatures and under-nail temperatures.  It was assumed that they'd have lower core temps because of their lower skin temps, but researchers were wrong.  The lower skin temp is due to higher vasodilation to shed the extra heat, which is very effective.  Even quite obese people in saunas don't have a higher temperature spike than normal-weight people.  They just sweat more.  This shows that they could maintain a "normal" core temp if that was a priority.  They really do have a higher rate of homeostasis-targeted thermogenesis than smaller people. More evidence:  The thinner you are, the lower your core temp.  Underweight people have even lower temps then normal weight people, and that continues all the way down to death.  And we're absolutely sure that thinner people with low body temps have nothing to do with a lack of insulation but rather a metabolic downregulation in response to perceived lack of nutrients.  It's part of the cornerstone of the theory behind calorie restriction's effects on longevity. So although it was once believed that "naturally fat people" would have "lower metabolisms" at a given weight than "naturally thin people", largely due to studies of "calories out" with doubly labeled water, with the advent of activity trackers, we now know that the difference in calories out is due to NEAT--activity thermogenesis--not basal metabolic rate.  "Naturally thin" people walk, fidget, move, pace, etc., more than "naturally fat" people.  As a thin "naturally fat" person (meaning that I burn WAY less calories than a sedentary lifestyle should--halfway between my basal and "sedentary" number--without deliberate intervention), understanding that my tendency to work in a single position for many hours was killing my metabolic burn helped me make environmental changes to bring my base burn without exercise up past sedentary.  With my horrible level of activity, I would have gradually become obese eating 2000 calories a day.  And I'm not even short.