Why are South American tribal people so fat?

I blame it even more on the sugar that is in everything. Fast food isn’t as bad as the 16 oz fountain sodas with free refills that it’s washed down with (although the burger buns are a custom extra-sweet bread). As someone who is currently on a low-carb diet, I can tell you how hard it is to find any processed food that does not contain sugar in some form, with the near-universal presence of “dextrose”.