In trendy, hipster London or New York, it’s all about juicing, vegan diets and snacking on kale crisps. Thousands of miles away, in Nairobi or Bogota, the middle classes are more likely to reach for roasted goat or a juicy steak. Later this month, world leaders are set to endorse a U.N. goal to eliminate hunger by 2030, but they will have to convince their citizens to adopt new eating habits first, experts say. Diets…