Yes there are tribes of people all over the world that can eat nothing but dairy (usually goats) or how about those Africans that drain blood from their herd of cattle and eat that ? It is their mainstay protein and has been for thousands of years....it is what they have evolved to be able to digest.
Some people can live on bugs...But in this day
I can drink goat and sheep's milk all day long, but I cannot even LOOK at cow's milk without getting blaoted and very pain-ridden.
It is not a sensitivity, it is my immunal system that can see that is from a cow, it reacts and attcks, and in the process, scalds the intestine, throat and esophagus.
What we have today is called GLOBALIZATION...in which every race is in one country eating a bunch of crap that their intestinal systems have never seen before...and each of us is hurting from this.
We need to eat what our bodies have evolved to eat..and give our bodies time to evolve to digest fast food and the other crap here.
If I ate nothing but a 19 century Scottish farmer's diet, I would not ever be sick.