well if the fat buddha name fits?. . . . .
seriously though, clearly they are not, but by a normal weight to height ratio it would appear as such on one of those simple BMI calculators that don't really tell the whole picture!
try putting in 18 stone and 6ft on this one and see what happens
http://www.bbc.co.uk/health/tools/bmi_calculator/bmi.shtml
I can join you as well cos at 5'4", and a size 12, i am 11 stone - this means i am overweight. (mind you i only have to lose a couple of lb and i am 'normal' - whatever that means. . . . )