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The Fat Burning Zone: Myth Or Reality?

February is Heart Healthy Month, and today is part 3 of a 4 part series on Heart Healthy Exercise! Fitness Together's cardiovascular programming recommendation is that your weekly cardio efforts will include:

  1. One short duration, high intensity event (SDHI)
  2. Two moderate duration, moderate intensity events (MDMD)
  3. One long duration, low intensity event (LDLI)

Two weeks ago, we started things off with your long duration, low intensity workout. Last week, as it was Valentine's Day, I touched on the hottest heart rate training zone ... Zone 5.

We'll tackle Moderate Intensity, Moderate Duration next week. This week, however, I'd like to slow things way, way down and comment on the coolest of the 5 heart rate training zones, Zone 1, also known as 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 cardioeffort 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't the 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 simply pick it up a bit! You need to get OUT of that fat burning zone!


You see, energy for activities and exercise always comes from a blend of fat, carbohydrates, and proteins. In the Fat Burning Zone ... where you are operating at 60% to 70% of your Max Heart Rate ... energy requirements do indeed allow for energy to come primarily come from fat metabolism. However, for fats to be used as an energy source for exercise (or activities that aren't too rigorous), they must be first converted to a more usable form of energy called glucose. And as 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, as you increase your exercise effort, the utilization of fat as an energy source quickly 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 more calories as you pick up the pace within the Cardio (3) and Anaerobic (4) zones, but that energy will come from carbohydrate, glucose, and glycogen sources .. not fat!

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: 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.


If you're curious about learning more about The Fat Zone Myth, just send me an email to request a full copy of my Heart Rate Zone Training to Look and Feel Fantastic

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