South African high fiber diet decreases cancer risk, American high animal protein and fat diet increases cancer risk. What if these 2 study groups swapped diets?

When the South Africans swapped diets with the African Americans for 2 weeks, their colons showed markers consistent with a higher cancer risk. When the African Americans swapped diets with the South Africans, their colon cancer markers diminished. See the article: http://www.nature.com/ncomms/2015/150428/ncomms7342/full/ncomms7342.html