Some people, when you hear them talk, you can just tell that they're fat without even seeing them. The Notorius B.I.G. is a good example of this. That voice could NEVER emerge from the throat of a skinny person... it would simply be impossible. What is it about fat that changes a person's voice? Does it provide some kind of muffling effect?
certain states of estrogen excess lead to endogenous obesity
I can think offhand of two popular singers of an earlier era, Rosemary Clooney and Barbara Cook, who started off very skinny and became extremely heavy. I don't recall it changing the quality or sound of either of their voices.
I think being a bit bigger as an opera singer helps strengthen the diaphragm / support muscles, since singing is largely about air flow and support. My take is that skinny people can strengthen those muscles, but fat people will naturally have stronger support muscles than skinny people. It is probably more of a weeding effect, that fat people are more likely to have it easier starting out as a singer, so fat people end up continuing and succeeding as an opera singer more often than skinny people. I don't think that being fat changes anything about vocal resonance.
You say "Gimme a burger" much more often.