This series of blog posts is a fascinating read into conjectured factors behind the obesity epidemic. I wish the author had continued their rigor in reasoning throughout the two blog posts. Step by step the author is lured into proving a single factor explains the rise in obesity. That maybe a futile attempt from the outset. To make an example, the author notes, correctly and to the point, > "Calories are involved in…
Others have mentioned gut biomes... My uneducated guess is plastics or some other chemical that was introduced into industrial use in the 20th century. The cross species effect (lab and zoo animals getting father on the same controlled diets) is also a really big clue that were dealing with a molecule. And, as with lead poisoning from gasoline, perhaps a hard to pinpoint one due to prevalence.