Burning body fat while exercising might be a huge motivation for you to start with any kind of endurance training. But if you go about it in the wrong way you will not get the desired result and investing any of your time and effort into your running will be demotivating.
Uncovering the secret of fat burning will add to your training success and you will not have to believe in all those strange body fat burning myths anymore.
Where does the energy come from?
As simple as that: To make your body to run, your muscles require energy. More intense activities burn more calories. But this does not mean that you slim down faster when running at high speeds all the time. Mostly, the opposite is true as I will explain further on.
The energy (calories) your body burns, come from two main sources: carbohydrates and fats. Imagine that as two separate batteries for your mobile phone.
Carbohydrates (carbs) are your small phone battery with a limited life span. They are mostly provided by food like bread, pasta, sugar or potatoes. Carbs are stored in your muscles, liver, and blood (in form of glycogen). Your body loves to burn carbs because they are more easily available than fat, but the size of the carb-storage is very limited, only about 1,700 kcal. Burning mainly carbs has two big disadvantages: a) your body burns less fat (or no fat at all) and b) your endurance will be quite limited because you are only tapping the smaller energy source.
In contrast, the source of fat is virtually unlimited. About 80,000 kcal are stored in an average sized slim male body. That equals about 47 times the amount of your carb storage. Obviously, this is your big battery which can help your phone to last for days without charging which means it allows your body to run for a long duration without getting tired. Fat is stored under your skin, between the organs, and in your blood. But as a downside, our body does not like to use fats as they are much more difficult to convert into energy. As a consequence, you have to teach your body how to use the unlimited big battery of fats while saving the small battery (carbs) for an emergency.
Your fuel: Carbs & fats
The energy your body burn is – most of the time – a mixture of carbohydrates and fat, but depending on the intensity of your activity, the supply contains different portions of both. Unfortunately, burning fat is not as easy as recommending a perfect speed or heart rate for you, because your metabolism is highly individual.
To illustrate the energy supply while running with continuously increasing speed (5, 6, 7, 8… km/h) the 2 following pictures show examples of metabolisms [Pics A & B below]. The green area shows the percentage of fat metabolism at different speeds [FAT] while the red area shows the burnt carbs in percent [CARBS]. Both parts of the energy supply (green + red) always add up to 100% of the required energy.
At a lower intensity, your body is able to burn more fat (green) and therefore, it requires fewer carbs (red). But the faster you are running, the less is your body able to use fat as an energy source (down to 0%). This means, more carbs are needed to cover the extreme energy demand when running at high speed (up to 100% of the required energy).
The metabolism of each person is unique and if you compare pictures A & B, the differences are easy to spot.
This means that of two runners, both might use a different energy mix while running at the same speed. Imagine, both people will be running at a speed of 8 km/h and intend to burn some body fat (which would be one of the aims of basic endurance training).
For person A, the usual running speed is an easy jog which contributes to the aim to burn fat and increases endurance (pic A: burning 50% of body fat and 50% carbs which is exactly the point where the red and green line are crossing).
But for person B this run is hard work and the body has to use 100% carbs to be able to cover the required amount of energy. In this case, zero calories are being burnt from fat (0%) and whereas the carb storage will be depleted after the run, he will be low in blood sugar and very very hungry (pic B). His body strongly requires fuel and he will easily eat double the amount of calories he just ran off. However, this is not beneficial if the aim is to lose body fat. And besides: The training effects of running based on fat supply and running on carbs are completely different. (Look forward to the following blog post about designing your running training).
How to improve the fat burning?
The secret to optimizing your fat metabolism is to train in the right heart rate zone.
The perfect training zone is the speed or heart rate zone where your body is already able to burn fat. Working out in this optimal zone increases the ability to use fats more efficiently even at a higher speed and lead to easier runs without feeling exhausted afterward.
How to figure out the right Zone?
Performance testing is the gold standard of sports science and applicable to every fitness level. Testing by ergospirometry[*] delivers the most accurate results by measuring your breath while running or walking. This testing includes a detailed assessment with recommendations for heart rate and speed and your individual training zones.
[*] Just let me know if you are interested in a performance test on the treadmill or bike, individually adjusted to your fitness level and running goal! If you are living in Singapore I would love to arrange a test appointment at your convenience. Just send an email for further information: firstname.lastname@example.org.
But in case you should not have the chance to perform this test, observing your breathing is still better than having no idea about your best running speed at all.
A general rule of thumb: If you could talk to your neighbor while running (whole sentences, not short at breath) you are most likely in the right zone where you are burning fat.
For most of you, this will probably mean that you will have to slow down quite a bit for any basic endurance runs.
It might feel easy for your body because you are used to running at a higher speed, but remember: For your metabolism, it’s hard work to learn how to burn fat. If you are not exhausted after the run, you did it right!
Here are some further reading recommendations for runners (click the link below):