Even here, very very thin--there are mouse models of very very thin that result in fattening of the liver and insulin resistance. It's not the getting fat, there are models where increasing ability to trap fat subcutaneously decreases central insulin resistance. Central visceral obesity is something that can be measured with a tape measure, but fattening of the liver itself cannot--and in the case of the pancreas itself, levels of pancreatic fat supposed to cause insulin resistance and beta and alpha cell dysfunction is measure in grams, single digits.