Vietnamese are in large part lactose intolerant. When people started getting a bit more prosperous most quit cooking in the yard over fires that were never extinguished. The kept pots of bones on that fire when not cooking and periodically added wood underneath and water into the pot. They used the bone broth in cooking and the kids all grew up they got plenty of calcium. Between 2005 and 2010 most of the folks in my town switched to bottled gas two burner rigs and the bone broth disappeared. I was shocked when I went back in 2010 and most of the small children had black or stubby teeth. No calcium in the diet. The own had prospered enough to buy the gas hotplates but lost the bone broth in the process. It is way too expensive to keep those pots going full time on gas and they were not yet eating more meet. The urban areas have had rapidly rising prosperity and the diet is much more carnivorous, more food generally and you don’t see all the bad teeth on the little ones now. And I am going back again this fall.
Interesting. A little early, but have a good trip. :^)