There actually is but can not apply to fatties. Fat's actually have very high metabolism. The first reason is that it takes a lot of energy to support 10+ gallons of living lard. The second is that the body doesn't want to be that fat so it tries to generate more heat to waste energy. That's one reason that they're always sweaty. Metabolism is dictated by leptin levels and fats test at very high leptin levels. There is a starvation mode but it only applies to people who are starving aka nearing essential body fat levels 10–13% women 2–5% men. Fats can actually fast for days/weeks/months without dropping metabolism once their body becomes adapted to burning fat (because their body is so fucking unfamiliar with doing so). TLDR: Fatties lie and fuck up physiology knowledge for everyone else.