Not so according to a growing body of research that shows that even if you eat the recommended amount of servings in the food pyramid and exercise for an hour it is not enough to prevent obesity and heart related diseases. The number one culprit/public enemy number one for the onset of such diseases is sitting?! How could such a mundane activity such as sitting be the leading cause of obesity?
The scientific explanation is that we have special enzymes in certain muscles of our bodies that never tire when we stand up, and one of those enzymes called lipoprotein lipase converts fat into energy and LDL (the bad kind) into HDL (the healthy kind). When you sit, those muscles that are used while standing are relaxed and enzymes like lipoprotein lipase are essentially shutdown, allowing fat and LDLs to collect and build up in the bloodstream. Indeed, sitting is the second most passive activity (Sleeping of course is the most passive). What's surprising is that the people who workout everyday and eat a balanced diet but sit a lot still have obesity problems. It's as if sitting negated your workout.
Now don't jump to the conclusion that sitting is evil and that I must stand all the time. The problem is that the average American spend about 9 hours a day sitting. Lets assume that you had 8 hours of sleep and an hour workout. In those remaining 15 hours, you still need to burn the majority of your 2000 calorie diet. (Unless you are Michael Phelps who can burn 1000 calories per hour). Sitting for more than half of the remaining 15 hours will not get you to break even point, and slowly the daily excess calories accumulate around your waistline.
After I finish a meal my parents often tell me to stand up for about an hour and their reason is, "because it's good for you." I would ask for further explanation and they would reiterate their statement in a different form: "because sitting after a meal is bad for you." Since this was such a minor thing, I did what was told without inquiring further into the matter. A few years later I find out that my parents were right after all.
My personal guideline is to stand up every other hour. I know this sounds weird but I put my laptop on a ledge that is adjusted comfortably to my height while searching the web, watching Youtube clips and writing this post. Not only is standing healthy but it helps me not fall asleep, especially if I need to stay late to study for finals.