[gaius]

It's more subtle than that. The difference in attitude between "I walk when it's unavoidable" and "I walk whenever I can because we spent a billion years evolving to do it and living in a city is very bad for my overall health and wellbeing".

[palish]

There was a woman who became obese following a transplant of gut flora.

Recall how much the idea of evolution bothers some people. Are you sure this isn't a similar type of situation?

We seem to have evidence that obesity isn't always a choice.

[gaius]

For 50% of the population? I call shenanigans.