If high-carbohydrate diets contribute to obesity, why haven't East Asians historically been faced with it?

It might have something to do with high calories AND carbohydrates. I only say that because I'm visiting Ghana right now and they eat a lot of things that are high in carbohydrates with pretty much no vegetables and I'm almost positive I've lost weight whereas if I were in the US right now eating the same way, I would have most surely gained a bunch