HaLevi:Uneeq, the source of this Sakana is some 14th century doctors. The proof that it is not a Sakana now is today’s doctors.
I asked for a source and you tell me that today’s doctors say it’s not a sakana. I’ve never seen a tshuva that quotes modern doctors and I doubt you have either. Also, you would have to show me where there are studies that all different combinations of fish and dairy are not unhealthy. And while you’re there find me a study that says eating fish and meat is unhealthy, which I doubt you have seen either, but still doesn’t stop you from keeping that “minhag”.
Bottom line: If you have no have no full proof that something is NOT sakana, you would have to follow your Mesora on what the great Poskim held. That is why no one would eat fish and meat these days, even if no doctors cite it as being sakana. By fish and dairy however, being that I’m Sephardic, I go after Maran that nobody has proven wrong yet. (By the way he’s 16th century not the 14th).
If your Ashkenaz, you can go after the Darkei Moshe, Shach and Taz that all argue and hold there is no sakana.