Weight loss myths: the fat burning zone

"Exercising at a lower intensity for longer is the most effective training for weight loss".

Have you heard this before? I find myself discussing this misconception frequently, particularly with new clients who are trying to understand the philosophy behind the training programs I prepare for them. The 'fat burning zone' is possibly the biggest myth surrounding training and weight loss, up there with 'spot reduction' and 'lifting light weights with more reps for toning' (we will get to these another time). Don't get me wrong, endurance training is obviously necessary for the endurance athlete. What I don't agree with is endurance training as the main exercise method for weight loss. Why? Because it doesn't work. Why not and what should I do instead? Read on...

The Myth

The 'fat burning zone' myth suggests that exercising at lower intensities, in the 'fat burning zone', is the optimal training method for losing body fat / weight". FALSE! So, if this isn't true how did the myth of the 'fat burning zone' start? Fair question. The theoretical 'fat burning zone' does exist however it's been misinterpreted. To explain, I'm going to give you a very brief exercise physiology lecture. Here we go!

Your body is constantly burning (metabolising) a combination of both stored carbohydrate and fat. This is happening all the time, even right now as you're sitting there doing nothing. Fat is slower to break down (metabolise) and therefore slower to release energy, making it the preferred fuel source at lower intensities. Carbohydrate is much faster to metabolise and release energy making it the preferred fuel source at higher intensities. Up to an exercise intensity of roughly 60-70% of max heart rate (low-moderate intensity exercise) fat is the predominant fuel source for activity. As exercise intensity increases over 70% of max heart rate (high intensity exercise) carbohydrate takes over as the predominant fuel source. This has led to the misconception that exercising at a low intensity where fat is the main fuel source is the most effective method for fat / weight loss.

The Facts
It's the total energy 'burnt' that contributes to fat / weight loss not where the energy comes from. It is true that a  greater proportion of the energy 'burnt' comes from fat during lower intensity exercise however at higher intensities a greater total energy is 'burnt' and this is what's most important.

Fat / weight loss is not only the result of energy expended during exercise sessions. The energy the body burns constantly at rest is far more important and determined by metabolic rate. In addition to a greater total energy expenditure during exercise, high intensity exercise results in a greater post exercise energy expenditure and a greater increase in metabolic rate then low intensity exercise. Frequent low intensity long duration exercise can actually result in an adaptive response which slows the metabolic rate. This is done to increase the body's efficiency of storing and preserving body fat.

In summary, weight loss results are determined by total energy expenditure. When compared with exercising in the 'fat burning zone' (low intensity), high intensity exercise results in:

• Greater total energy expenditure during exercise.
• Greater post exercise energy expenditure.
• Greater energy expenditure at rest due to increase in metabolic rate.

These results are why I incorporate high intensity exercise into my personal training sessions and my own training. Low intensity exercise sessions have their place but only as a small component of a fat loss program where high intensity workouts are the majority. Forget the 'fat burning zone' - focus on shorter high intensity workouts for better weight loss results and long term weight control!