I read a study in Good Health Australia about the fact that thinner people tend to be more "fidgety". But they added that thinner people just move more in general - walking when they talk on the phone, tapping their feet when sitting, and generally being unable to sit still.
They didn't say why but I assume it has something to do with metabolism and energy and all that.
I'm not sure if you can artificially fidget if this is not your tendency though.
It's probably something like an extra 10-100 calories in a day. I wouldn't track it or anything.
I heard something about it.
From what I understand, any movement burns calories and the more you move the more your metabolism will increase and the more you'll burn.
There has been quite a lot of research done into this and there was a great programme on the BBC recently called "The Truth About Exercise"- http://www.bbc.co.uk/programmes/b01cywtq . You may not be able to watch the actual episode if you're not in the UK, but may be able to find it on YouTube. The series is science-based and is called "Horizon".
And here's a review of the programme that may answer your question about fidgeting - http://www.guardian.co.uk/tv-and-radio/2012/f eb/28/horizon-the-truth-about-exercise
The chair is a killer apparently.
I don't know any medical data or facts about this. However, my mother has never worked out and eats like every meal may be her last. She also loves her bowl of ice-cream with candy at 9 pm every night. The woman is a fidget machine, complete spaz and OCD with the cleaning. 5'7 115 lbs from the age of 20 - 69. Actually, now at 69 she's more like 5'5 and 110. Oh and she has an hour glass figure, not model stick build.
Man, how I wish I inherited the fidget gene.