[smolder]

To say even most modern disease has to do with carb intake ignores all the diseases that clearly aren't even diet related. You could probably get away with saying most diet related diseases are related to carb intake. I'd say that's a stretch, too, though I do suspect, as you do, that the type and quantity of carbs people eat is underappreciated as a factor in many illnesses.

[glastra]

Yes, absolutely. Some diseases are due to pathogens and such. But those should not be "modern", in the sense that said pathogens might not be exactly new. Maybe you could say anthropogenic diseases such as lung cancer from smoking or esophagus cancer from drinking are modern, though.

What I meant by "modern diseases" in my comment is a group of non-communicable diseases or so-called "diseases of civilization".

"Diet-related" is rather ambiguous, so different lines might be drawn there. As an example, would you say Alzheimer's is a diet-related disease? What about melanoma and/or sunburn?

[smolder]

Ah I either missed or misunderstood the use of "modern" there. I can't speak to the relationship between diet and melanoma or Alzheimer's, but I understand your point.