But I've never seen a tiger wearing contact lenses or glasses.
Does that mean that all tigers have perfect eyesight?
Or a rhino in a wheelchair,
or an elephant with a sling,
or an anteater with a toupee,
or a crocodile on crutches!
No, this means that these other animals have neither the means nor the intelligence to deal with the problems - they either cope with it or die out - you can't say that if an elephant doesn't make itself a sling it doesn't have a broken leg.
As far as I'm concerned, being fat is not a disability - yes certain people may be more inclined to increase in size compared to others, but then that's life and you just have to watch what you eat.