At high body fat levels your body is rather cavalier about burning calories. Triglycerides practically leak out of your bloated fat cells and your blood is chock full of fatty acids, sugar, and diabeetus. Body heat is a good example of this, ever notice how fat-asses always want the AC on? Their chubby little mitochondria just keep humming along with all that sugar, keeping those flabs hot and sweaty.
The reality of it is that the very phenomenon that fat people claim means they can't ever lose weight (because as their weight drops their energy reqs drop) is actually their bodies trying to keep them from making that final push from obesity to morbid obesity.
The reality of it is that the very phenomenon that fat people claim means they can't ever lose weight (because as their weight drops their energy reqs drop) is actually their bodies trying to keep them from making that final push from obesity to morbid obesity.