Well they do but it's due to malnutrition. I've seen quite a few vegans having strokes and heart attacks young, in fact an ex-girlfriend had a heart attack at 28 due to veganism, she was/is slim. It's also common in skinny endurance athletes who eat high carb diets to have heart issues. I think people don't realise that fat people are still malnourished despite the amount of calories they eat.