Will americans evolve to become less prone to eat sugar and be more resistant to them ?

I've heard the argument that black people in USA has better genetics since slavery killed "the weakest ones". A similar argument is used to explain why nordic and slavic women tend to be prettier since "the ugly ones were killed while the brutest vikings raped the hottest ones". It's also known that africans and europeans have different immune systems that are more adapted to diseases related to their local regions

I don't have scientific proof or papers to back what I've said so far, so feel free to counter argument any of what I'm saying. I was wondering if due to natural selection americans that have digestive systems that are more capable of processing "bad foods" (i.e, beverage drinks, refined sugars, saturated fats, carbs... ) and at the same time, people that segregate less dopamine when being fed such foods, will eventually be more prepared for living in such an environment