[nevinera]

That direction of thought has produced quite a few useful insights, and continues to drive significant research. I'd never call it a 'fundamental truth' though - it's a question, and a type of question which allows for many interacting answers, none of which may be fundamental. In particular, it can be extremely difficult to trace the links between societal (non-physical) changes and the mechanisms by which they affect the physical.

We are eating more sugars - is that because more sugars are supplied, because we can afford more sugars, because sugars are snuck into all our foods, or because we like sugars more than we used to?

We are moving around less - is that because we have more sedentary jobs, because we have less physical labor to do at home, because the interesting hobbies that don't involve moving around are expanding, or because some quirk of the childrearing techniques in the 70s had significant impact on our interest in athletics?

You see how complicated these things get when you start talking about 'fundamental' causes and reasons.