I entirely agree, Lottie. People have always figured that fatness was inheritable, but in recent years it's been seen as purely a matter of diet/exercise.
In my own family I took after my father (in colour, temperament etc); he was thin but grew fat, and so have I. My brother took after my mother; she stayed thin and so has he. You could quite reasonably explain the difference between my brother and me as down to diet and exercise, as Loosehead suggests (he played badminton for his country and works outdoors; I'm a desk jockey and more the stamp-collecting type).
But you can't explain away the differences between my parents so easily. Their wedding phtots show them exactly the same size and shape. They had the same diet (meat and 2 veg, neither junk food nor lo-cal) and the same amount of exercise. The way their weight diverged can only be down to genetics.
The way their kids also diverged was no surprise to any of us. After all, the whole idea of 'taking after your parents' is about genetics.
But it's been irritating the last 20-30 years the way thin people are seen as normal and fat people as weak and wicked, and obesity as a 'problem'. Fat is as normal as thin; humans come in a variety of shapes and sizes, that's the way life is. If scientists are belatedly proving this, well, it's about time.