Yet in just a few months I feel my posture improving since I started psychotherapy and somatic experiencing therapy for trauma. Along with that I go to yoga once or twice a week. It's importnat to note here because I see the cogs spinning already... I actually did yoga years ago and did not notice the same effects. Therapy has been key to the changes I've observed in my posture.
My conclusion is a lot of bodily tensions are connected with unresolved emotional charges. This is related to the nervous system at some level.
My point is that posture, and general routine is symptomatic of your general emotional wellbeing.
As with all things in life, moderation is the key. Just doing a 1h30 yoga class once a week will probably offset much of the problems mentioned in the article.
I mean, I've sat at a computer (both for passion and work) for the past twenty years and have NEVER been fat. In fact I was underweight due to anxiety. I put on some weight in the gym in my early thirties which 70% have stayed without doing any regular exercise (which further confirms a health issue symptomatic of emotional / nervous system troubles affecting appetite).
I suspect that improving posture and making an effort to keep a good posture goes a long way also to offset the problems of sitting.
Don't get me wrong.. I can see in yoga class that sitting a lot has made muscles between inner thigh and pelvis very tight, as well as all the front making it diffuclt to stretch in various postures.
The problem here is assuming that N hours spent sitting equal N equivalent "damage". But that's not how our body works. It may be that you only need a good gym or yoga session just once a week to offset much of the problem. Not that it "undoes" the damage; but rather seeps into the rest of the week with more tonus in posture, and more postural awareness.
TLDR: context. Nobody gets fat because of sitting. If weight is really an issue I would suggest to seek therapy or if you feel that is not needed, try yoga or massage. Anything that takes you out of the left hemisphere's imbalance (cf. "The Divided Brain" by Iaian McGilchrist), and nurture more being in direct contact with the body, sensations, breathing.. as well as being more connected with others outside of intellectual activities. Surprisingly a lot of people think that "socializing" means talking. No, to be truly with others around you, is to be able to be there instead of taking refuge in the mind. That means to be at home in your body and how it feels. It's a journey.. it doesn't need to be taken in a couple days ;)