Can't beat this drum enough. Consider using a treadmill desk. Alternate between sitting and walking. Moving is better than standing still.

See my setup. https://www.dropbox.com/s/089qqvaa7j5ob77/office_setup.jpg

I've lost a lot of weight with this setup. Still have a long way to go.

I've found the key to concentration is walking slow. It has a max speed of 4MPH (which is way too fast). I walk at a pace of 1.2 - 1.4 mph. I walk in segments of 25 minutes. Break for 5. Longer breaks every 4 cycles. (Pomodoro Technique)

I look at this as in investment in my health. It's paid off already, in big ways.