This is interesting. I’ve read about this before, but didn’t take any notes on this thus yet. Studying digestive system microbe changes in immigrants? First of all, people outside the U.S. in developing and third world countries tend to have a greater diversity in gut bacteria than U.S. people and people of western diets. Now, here’s the interesting part. After immigration, after only 6 to 9 months, the immigrant’s gut bacteria changes drastically. Most of the native bacteria they had is lost, and they acquire the new bacteria that is more common among western diets. The process continues on even for 10 years. For the children of immigrants, the shift is more drastic. Shifting to a diet of western foods somewhat explains the change in microbes, but it doesn’t completely explain it.
Additionally, one peculiar association with studying immigrants is that in their original conditions, obesity levels are very low, but after migrating, obesity becomes a larger problem. There is still a lot unknown here, but it appears from the diagram in the article that what happens is that in the beginning, obesity is less of a problem for immigrants than it is for westerners, but after immigrating, it becomes just as much of a problem for them as it is for westerners.
20181209/https://cse.umn.edu/college/news/immigration-united-states-changes-persons-microbiome