My point is that people's health has been rapidly deteriorating over the last 30-50 years especially. Your attempted explanation is essentially, "in every prior period, there was a different period-specific thing that was preventing these health outcomes."

It seems far, far more likely to me that right now is the aberration – in fact we know today is aberrant on several dimensions that are presumably related to obesity, so that's where we should look.

Big, system-wide changes like what we're experiencing are almost always both multicausal and overdetermined.

The causes here are:

1. Production of cheap, extremely palatable, ultra-high caloric density foods (mitigable). Note: This is not the same thing as saying "people used to be thin because they were starving." It is absolutely possible to feed a country amply and not yield the low price/great taste/horrible nutrition profile that dominates the American diet today.

2. Increase in sedentary time due to shift from physically intensive professions (not very solvable), car-centric urban planning (solvable), and the dominance of ass-in-chair leisure activities (probably mitigable)

3. The science is early on this but there's good reason to look further into endocrine-disruptive chemical poisoning (mitigable). We are finding these compounds absolutely everywhere we look and we should be very open to the possibility we are mass-poisoning people and damaging their metabolism: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10003192/