It really isn't.
<{POST_SNAPBACK}>
Whatever. You can listen to some guy on the Atkins diet or someone who is actually in shape.
I am a runner, but that works for me because of my lithe build. Like Brian and Sass said, though, a lower impact form of cardio is probably better for most.
A combination of cardio & weights has worked very well for me for several years now. I can run competitively in local 5Ks, bench press considerably more than what I weigh, and my body fat is very low (6-7%).
And fuck low carb dieting, you need carbs (clean carbs-->whole grains, veggies, fruits, etc.) if you intend to be athletic in the least.
If you want 6-pack abs, don't do a trillion crunches like an ass. Burn off the fat with cardio, amp up your metabolism with weights, and lay off the cheesecake. You will lose that padding across your stomach. Then you can jack up your muscles with some simple weighted crunches or other weighted abdominal exercises.