The Cardio Myth

The "Cardio to lose weight" idea has never worked...but we kept on doing it anyway

Aimee came to see me for a weight loss program. Two years ago she joined a gym to lose weight and has built up to walking on the treadmill for about 2 hours each day. All she has managed to do in 2 years is put weight on - 20 kilos in fact! She believed that cardio exercise was going to make her lose weight. I've managed to get her off the treadmill and into something different. Now she's losing weight at an average of 1.6 kg per week.

So what is cardio exercise and why do we think it makes us lose weight?

Low-intensity exercise such as walking, jogging, easy cycling etc has been termed "cardio exercise." When you exercise, your heart rate goes up according to the intensity, therefore you are training your heart (cardio). One day some scientists decided to do a study. They got some athletes together and they tested their blood samples at different intensities of exercise. They found that at low intensity (cardio) - walking/jogging/easy cycling etc their body used more fat than sugar for fuel. At high intensity - running/sprinting/cycling up a hill etc their body used more sugar than fat for fuel.

From this study, a number of assumptions were made...

"Everybody wants to lose fat so we should train at low intensity because that's the 'zone' where you burn fat!" Others got hold of the idea and called it the "fat burning zone." In no time treadmills, stationary cycles, rowing machines and all manner of "cardio" equipment soon had heart rate monitors so you and I could exercise for hours in "the fat burning zone." It wasn't long ago that you would have been lucky to find more than a single treadmill and a few stationary bikes in your local gym - next minute there are 20 of them all lined up in rows facing a big TV screen.

At first glance, the idea of exercising in the so-called "fat burning zone" sounds like it makes sense, but let's take a closer look at what is really going on. For starters, the "fat burning zone" is low intensity which means you are only burning a low amount of calories. So even if you walked two and a half hours you are only going to burn the calories of a small meal. To lose weight you would then have to walk another two and a half hours to burn the extra 500 calories needed to achieve weight loss. By now you have walked 5 hours, burned off the last meal and got yourself into the deficit required to lose weight.


But your body isn't stupid.

Do these long walks on a regular basis and pretty soon your body will adapt. Muscles and metabolism will change so that the regular walk is done with less effort. It's called getting fit - in this case fit to walking! That's cool - nothing wrong with some walking fitness. But hold on what was the goal here? Oh yes - to lose weight. Somehow the initial weight loss has come back on again! You are fitter but not lighter.

What happened?