The Fat Burning Myth

February is Heart Healthy Month!

Last week, as it was Valentine's Day, I touched on the hottest heart rate training zone, Zone 5.

This week, I'd like to slow things way, way down and comment on the coolest of the 5 heart rate training zones, Zone 1, or the Fat Burning Zone. While time spent in the Fat Burning Zone has it's time and place, one of the more common mistakes I see in clubs is the use of the Fat Burning Zone program on cardio equipment. Without knowing anything more, it certainly seems like a reasonable choice in cardio effort for a lot of folks: "I want to loose some fat; therefore, I want the Fat Burning Program. "

Unfortunately, spending a lot of time in the fat burning zone actually isn'tthe best way to reduce body fat! Nor is spending a lot of time in this zone the best route to good heart health. While time in this zone does have value in overall good health and fitness, you already spend most of your life in this zone ... when at rest ... when sedentary ... and when sleeping. Therefore, when exercising, it is critical that you pick it up a bit!

You see, energy for activities and exercise always comes from blend of fat, carbohydrate, and protein. Normally 60% to 70% of your Max Heart Rate, energy requirements for exercise in the Fat Burning Zone do indeed allow for energy to come primarily come from fats. But for fats to be used as an energy source f0r exercise (or activities that aren't too rigorous), they must be first converted to a more usable form of energy called glucose. Also oxygen is required to convert the fat to glucose, this level of metabolism is also considered aerobic (with oxygen).

The rub though, is that while the Fat Burning Zone metabolism is in fact slow enough to convert fats to glucose, exercise in this zone doesn't require much total energy, and, therefore doesn't burn all that much fat. Furthermore, and to the point now, is that at some point the utilization of fat as an energy source tops out: Exercise faster and you won't burn any more fat. Exercise harder and you won't burn any more fat. You do, however, burn additional calories as you pick up the pace within the Cardio (3) and Anaerobic (4) zones, as the following graphic illustrates. Here, fat energy consumption is yellow, carbohydrate consumption is blue, and protein consumption is red. The sum of all colors is your total calorie burn.

Note that while the fat utilization tops out beyond the fat burning zone, carbohydrate utilization continues to escalate with increased effort. And this is why spending time in the fat burning zone isn't a practical way to loose fat, because, at the end of the day, it's all about calories. Calories Ingested = Calories Spent + Fat Stored. If you consume more calories than you burn, you add fat. If you burn more calories than you ingest, you loose fat.