The Fat Burning Zone Myth!

I came across this article the other day about the myth of the “fat burning zone.” I had been told, don't know who by now, but it has stuck with me that in order to lose fat you must exercise at low intensity. Many aerobic instructors have their clients exercise gently to stay in their “fat burning zone.” Some runners even run slowly in the belief that low intensity exercise is the most effective way to reduce their body fat levels. Yeah, that's what I thought!

The myth developed from the fact that when you exercise harder, you use relatively less fat and more carbohydrate. This led to the belief that to lose fat you need to exercise gently. Using this logic, since approximately 80% of the calories you use while sitting are supplied by fat, then couch potatoes would have very low body fat levels. The missing ingredient is that fat loss is determined by the balance between calories consumed and calories burned over time.

It seems the source of the calories burned during a specific workout is not as important as the number of calories burned.

Sitting burns 45 calories in 30 minutes
Walking burns 150 calories in 30 minutes
Recovery run burns 360 calories in 30 minutes
Lactate threshold pace (bloody hard run!) 540 calories in 30 minutes


Higher-intensity exercise is therefore better for losing fat because it uses more calories per minute. Put in a 30 minute recovery run and you may use 360 calories. Spend the same amount of time at a faster pace and you may burn 540 calories. If you burn more calories, you will lose more fat than if you burn fewer calories.

Lower intensity exercise, therefore, is only better for fat loss if you exercise long enough to make up for the lower number of calories used per minute. The key to losing fat, therefore, is to find the balance of intensity and duration that burns the most calories.

Okay, now I know all that, I think I have a fair mix of runs. These are mostly determined though by how I feel on the day and, of course, the weather!

This article originally appeared in Running Times Magazine