I am confused with the statement that there is no difference between Jew and non-Jew. There are genetic differences between nations. There are nations that do not tolerate milk or alcohol.
Maybe you mean that a non-Jew may convert and will he acquire Jewish traits? That maybe not what sources mean, giving a general statement about Jews in general … But even then, if someone changes his lifestyle from hunting & heavy drinking to sitting with a sefer and drinking weekly, his condition will change.
Another interesting question: absorption of iron is decreased when milk is consumed. Iron comes from meat that was historically limited … So, Jews might be better at absorbing iron, leading to major metabolic differences.