Interesting. I was sceptical about your first post, because it seems to defy basic logic/physics. If you are doing strenuous exercise, you are by definition burning more calories than if you are sitting down, and therefore (if you don't eat more) you will lose weight. i.e. if you're taking in the same amount of energy (by eating), but burning more, you will have less energy which will translate into lower weight.

But this seems like it's suggesting that's not the complete picture, because we're really talking about total lifestyle not just some isolated experiment. i.e. people sitting down all day are not really "resting" (possibly even if they're not working).

What is the book?

Back to your original question, if something challenges my preconceived ideas, I will usually try to consider those ideas. But only if it comes from a source I have some level of trust in, and the logic of the argument is explained carefully. It can be hard to find a balance between having beliefs that are too rigid, and accepting whatever ideas come along that sound interesting/new, but that's what we should ideally be aiming for.