The first page of the search results below will link you to 4 previous posts that address the importance of moving your body (being active) throughout every day.
   I am very passionate about this health behavior.  The upshot is that sitting for more than one hour at a time, no matter how active you are otherwise, no matter what you weigh, is linked to higher rates of several diseases (e.g. heart disease, diabetes), disease risk factors (e.g. abnormal blood sugars, high blood pressure) and all causes of death (all cause mortality).  The amount of increased risk is different based on your general health, weight and exercise level but extended periods of sitting are bad for everyone. 
    Remember when I taught my first college under grad course last fall?  On the first day of class (they were 3 hour classes) I explained this sitting/disease risk to the students.  Then I made sure that we always took two stand up and move breaks every class - even when we had guest speakers. {traditionally three hour classes contain one 15 minute break}  If the only thing my students took away from class was the need to limit sitting time - I have done them a very big favor.
   That brings me to Weight Watchers.  The program is also doing their customers a very big favor.  My sister, who is a successful loser/maintainer (almost 5 years now) attends Weight Watchers - more to support others than herself, I think.  Today she told me that her meeting leader gave a great, graphical presentation on this very topic.  And as is true, the leader emphasized that the "not sitting" is important for HEALTH above and beyond anything it might do for calorie burn or weight.  To be clear, sitting doesn't make you fat.  Eating more food than your body needs is the cause of weight gain.  Sitting DOES make you unhealthy if you do a lot of it.  We are learning that a lot doesn't mean the number of hours you sit in a day, but the number of minutes you go without standing.
  Search Results on Sitting from this blog, with research links.  HERE