I live in Iran, and here people strongly believe in Avicenna’s humorism (or what is thought of it in popular culture anyways.). It is believed on the level of it being “common sense.” For example, if you eat fish, milk, broccoli, and tomato sauce, all of which are “cold”, you’re supposed to balance that out by eating walnuts and dates. My personal impression is that there is probably some truth to this simplistic model of nutrition, as I see a lot of anecdotal evidence for it, but well, I like to see what science is on the subject.

Note that the humorism believed in here (Iran) is not a strawman; People don’t believe that humor imbalance is the root cause of all diseases. It is mostly believed that if you eat very imbalanced foods, you will have a significant chance of getting “unwell.” E.g., you can get stomachache, vomit or get a sore sensation in the mouth. (I am not actually very knowledgeable on the traditional lores here, and the different imbalances are known for different symptoms.)

I might add that both my parents are experienced specialized medical doctors, and they, too, believe that there is something to all this.

My personal “wishful thinking bias” in this matter is that I like the whole thing to be false. I generally dislike nutritional restrictions, and I dislike traditions and alternative medicine. :))

Cursory Internet searches did not lead me to good meta analyses on this subject. I just found unempirical denials that these beliefs are now considered pseudoscience. I personally suspect premature theoretical disbelief instead of carefully studying subtle effects.