Originally Posted by kakman
I see no-one has directly answered this so here's what I believe to be true.
Exercise burns both fat and glycogen. As intensity rises, the ratio of fat to glycogen being burnt decreases (less fat/more glycogen). After exercise, if you have excess fat, the body can still continue to function as it still has energy stored in that fat. Eat too much of the wrong stuff and the fat will be replaced.
If you burn all your glycogen, your body needs to replenish it - either by Protein conversion (see Pat's post) or by eating carbs. It requires this to be replaced to function normally again which is why I believe most 'experts' prefer 'fat calories burned' as being a better indication of what you'll actually lose. This is why some HRM's indicated calories burned and fat calories burned as separate items.
At the end if the day, having a calories in - calories out deficit is correct BUT over simplified. If you were to exercise at a level where you only burnt glycogen, how could you ever expect to lose that spare tyre of fat? And how on earth could you keep it up, day after day.
The original post was directed at people who wanted long term, sustainable, weight loss. No-one is suggesting people don't go out of the fat burning zone - although Richard Cranium would have you believe that. It's simply that the most efficient zone for burning FAT is the 65-80% range - and that has not been refuted.
// k
Get a clue and try using Google. If you Google "Fat Burning Zone" you'll find:
The Truth About the Fat Burning Zone
http://exercise.about.com/cs/cardiow.../aa022601a.htm
The body does burn a higher percentage of calories from fat when involved in lower intensity cardio exercise. BUT, at higher intensities, you burn a greater number of overall calories which is what you should be concerned about when trying to lose weight.
Also,
http://www.prevention.com/article/0,...4219-1,00.html
It's true that the body burns a higher percentage of calories from fat during more mellow exercise like walking and easy cycling. But, when you pick up the pace for a higher-intensity cardio workout, you burn a greater number of overall calories (which should be your focus for weight loss) and subsequently just as much total fat.
and,
http://www.washingtonpost.com/wp-dyn...2004Sep27.html
If you're trying to manage your weight, you should focus on how many calories you burn, not on what kind of fuel you're burning. In a given period of time you'll burn more calories by working out at a higher intensity (i.e., in the "cardio zone") than at a lower intensity (in the "fat-burning" zone).
and,
http://www.ezinearticles.com/?Fat-Bu...Zone&id=306481
Although the “fat-burning zone” uses a higher percentage of fat for fuel; you need to look at the big picture which is calories burned.
There are many more...
Bottom line: the Fat Burning Zone is a myth, and for weight loss it doesn't matter whether you burn mostly fats or mostly glycogen when you exercise (you'll be burning both anyway...it's not a freakin' on/off switch!).