Even if you're doing a couple hours of intense exercise every day, you're only going to be adding on the order of 1000 Calories to your daily usage. Resting burn for most adults is around 1500-2000, so that's ~3000. What do you consider "sufficient" exercise?

Michael Phelps needed 12,000 Calories a day when training. That's seriously "intense"! http://www.foxnews.com/story/2008/08/14/michael-phelps-12000...

Wow, that is intense. Way beyond what I'd call "sufficient" exercise though!

You're reading the word 'sufficient' in the wrong way. Sufficient to demolish calories, not sufficient to be healthy.