I have had this in spurts but I never made a connection with diet/exercise. I just wondered if I was somehow developing adult onset ADHD but now that you mention it....
This is a good thing, really. It would be great if you could harness this restlessness and burn off a few more calories with NEAT (Non-Exercise Activity something calorie burning, I forget exactly). I follow the Obesity Panacea blog, which is really into the big effects non-exercise activity can have -- especially since it is a much bigger portion of your day than deliberate "exercise" -- and they talk about this a lot. They once featured a neat contraption which is basically a set of pedals hidden under your desk, that are not actually hooked up to anything, but basically lets you fidget with your feet. (For some reason I can't find that page again.) Maybe you could rig up something similar, or do isometric exercises sitting in your chair; google "chair exercises" or "Airplane exercises". At the end of this post on OP they have a bunch of suggestions from readers on workspace-compatible exercise activities: Obesity Panacea
(My favorite is the advice never to walk somewhere without a piece of paper in your hand, that way people think you have an errand. Or a large envelope marked "confidential" in big red letters.
OP also says it looks like it might be the big muscles of the thighs and glutes which are crucial in this, there are medical studies that show they go into resting mode quite quickly and this might be key to the problems seen in sedentary work. Are there co-workers around who would be bugged if you just get up and do a couple of squats a couple times an hour? You could say you have a "bad back" or "poor circulation", people are usually pretty sympathetic about that, and it gives you a more OSHA-based excuse. When I get restless legs or back and can't interrupt my work (or am in a plane) I kind of do mini-squats, just planting my feet wide and raising my butt off the chair a little. It's not the same as walking around, but it helps.
If your work environment permits you could try rigging up a standing desk for a while, although I would probably try something which lets you move between standing and sitting. It could be as simple as putting your computer monitor and keyboard up on a stand or small, sturdy inexpensive coffee table (think IKEA or walmart). It's an idea which is getting popular now with the media coverage of how sitting for long periods can affect your long-term health, so you can find lots of creative ideas on the internet. If you have to print things, maybe you could move your printer to a place where you have to get up out of your chair (or some other routine activity you have to do multiple times in a day/hour).
The champion of them all, of course, is the treadmill desk. Does your workplace/company have a wellness program that is amenable to promotional stunts?