Totally agree with you both Nik and Lucy..

Lucy, this was also my first thought 'then why are so many runners slim'.

His book is due in a couple of weeks, he's posted an article with summaries and highlights which is gaining traction. I wanted to quickly point out, in the meantime, there are lots of other things at play which would make this one-track theory not 'add up'.

Nik, to your point too, his research is based on the Hadza society, who as you might know have been running 'for a living' for centuries and probably have different evolutionary mechanism. Lucy, this is why he focuses on 'running' but generically says if you work out your body compensates.