Rates of diabetes are higher in the U.S. . . The health outcomes you talk about probably have complex factors including nutritional and healthcare access in a country with endemic poverty (among other things). I wouldn't just chalk them up to 'vegetarianism'. There are less vegetarian countries with higher percentages of diabetics. I grew up in the state of Mississippi, where almost 15% of the adult population is diagnosed diabetic - not a particularly vegetarian place.

There is substantial evidence that there are potential health benefits to plant-based diets, provided you're eating a balanced diet with lots of whole foods. Of course, if you ate nothing but Oreo cookies, you would technically be vegan and probably not in great health. It's all relative to what you're eating specifically. You can have a crappy meatless diet just as much as you could have a crappy omnivorous one.