all the time. lack of appropriate/translatable preclinical models is one of the largest barriers to new meds. in practice, if you can't find a mouse that has the same disease its almost impossible to prove your cure works,, even if it would in humans
A Western diet is a transferable thing. Just like in the US we hear about the benefits of the Mediterranean diet or the lower rates of some diseases in Scandinavia or Japan. China has had KFC since 1987. Korean restaurants often have Katsu. Japan has Kobe beef and steakhouses. It’s not some nationalistic plot to say that certain regional diets or their influences on a population are beneficial or harmful in various ways.
I think given that 75% of americans are overweight and 40% is obese, certainly food would be a very reasonable first hypothesis of any neutral, objective scientist. I would be surprised if food you ate didn't affect energy levels, feelings of wellbeing, etc.