Not so much the fat but the process - Swiss meringue buttercream for instance
has the fat added to the meringue but only after the egg whites and sugar are heated and beaten until the stiff peaks form. So now you have me wondering about a caramel meringue - beating caramelized sugar into egg whites (to make divinity you beat in sugar syrup) so figuring out the portions and such so that it isn't divinity and isn't marshmallows - science geek in me coming out.