Its the amount of growth hormone they feed their cows - it gets into the dairy products and causes them to grow to unfeasibly large heights. Obviously they would then look stupid with very short heads. Its a well known affliction with the medical term van Nistelroysiasis. One apparent side effect of BGH (bovine growth hormone) is that it can lead to collapsed lungs in injury prone strikers, as we recently witnessed with SDJ (de Smet & de Hoovers, 2012). I think mine must be the correct answer as I am the only one who has provided a reference. If anyone wishes to read it its from the Journal of Dutch Growth Defects.
This is true actually. I remember meeting Obi wan and thinking he looked like a cabbage patch kid that had been run over by a tractor.. then reversed over for good measure.