A common scenario I find is someone trying to lose fat (they call it weight) under their own direction without getting great results and beginning to get frustrated with their lack of progress.
Usually they work on the principle that the harder they work, the better the results will be. They work under the pretense that the harder you work, the more energy you use (and therefore surely the more fat you’ll lose).
The important factor here is not merely the amount of energy you use (or ”burn”) but also where this energy is derived from.
The important factor to consider in maximizing your exercise session to metabolize as much fat as possible is to maximize the product of the amount of energy used and the amount of that energy derived from fat sources.
Lets look at two examples,
1. Individual uses 500 kilocalories of energy of which 30% is derived from fat sources. That’s 30% of 500 kilocalories or 150 kcal of fat used. (Approximately 16.5 grams of fat)
2. Same individual uses 400 kcal of energy of which 60% is derived from fat sources. That’s 60% of 400 kcal or 240 kcal of fat. (Approximately 26.4 grams of fat)
Who used more energy? The individual in example one, 500 kcal to 400 kcal. (25% more energy)
Who utilized more fat? The individual in example two, 240 kcal (or 26.4 grams) of fat used compared to 150 kcal, (16.5 grams), That’s 60% more fat used!
Why is this so?
Your body uses more oxygen to metabolize fat than is does carbohydrates. But metabolizing a gram of fat liberates much more energy than a gram of carbohydrate (around 9.1 kcal compared to 4.3 kcal).
It’s usual that you utilize a mixture of both fat and carbohydrate sources to supply your energy needs. The ratio of this mixture depends on many factors. Two of the more important are the amount of energy required and the amount of oxygen available.
Under conditions of relatively moderate amounts of energy required combined with a liberal supply of oxygen, you will metabolize a greater percentage of fat than carbohydrate.
As the energy requirement increases, (by working at higher intensity) it becomes increasingly harder to supply this energy from fat sources (remember fats require much more oxygen than carbohydrates), so your body shifts towards greater percentages of the more efficient carbohydrate, thereby using less fat in the mixture.
So whilst you’ll use more energy by working harder, (energy use is directly proportional to energy intensity) you might use more fat by working at a less intense level.
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Regards Kym
