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Burn, Baby, Burn!

Posted by on November 27, 2012

We’re working those beats. We’re sweating it out! We’re on a roll!

But what exactly are we burning?

I promised that I was gonna do a write up on our fuel sources, or rather, where do we get our energy from when we exercise  so here it goes. Basically, there are three: FAT, CARBOHYDRATES, PROTEIN. In short, we use a LOT of carbs, some fat and very very very little protein. And this is because of 2 factors – 1. How much energy they provide and 2. How fast they burn.

Carbohydrates are easy to burn. It is the easiest to burn out of the three and produces a decent amount of energy (approximately 4 cals per gram). It comes in the form of muscle glycogen which is stored in your muscles for fast metabolism and plasma glucose which is stored in your body fluids so it travels everywhere in your body.

Fat produces the most amount of energy (approximately 9 cals per gram). Fat comes in the form of muscle triglycerides which again are the fat cells stored in your muscles, and plasma FFA (Free Fatty Acids) which, again, roam about in your blood and other fluids. I know what you’re thinking. Why doesn’t my darn body use up all the fat, then? It’s because fat is incredibly slow burning. A lot more processes are involved in the burning of fat and that takes time. So running on fat will make you move slower.

Protein produces energy, but it’s not meant to. Protein makes the building blocks of all the tissues in our body. Imagine your biceps made up of little pieces of Lego, those are amino acids i.e. protein. The body only relies on protein when it runs out of carbohydrates to burn. They start breaking down the amino acids and this is how you lose your muscle mass.

How our body decides which fuel to use depends on the intensity of the exercise we’re doing. Look at this graph below (I took it from some slides from The University of South Carolina Aiken by a Doctor Brian Parr). The top two colours (Muscle glycogen and plasma glucose) are carbohydrates and the bottom two colours are fat.

Exercise intensity which is measured in VO2 max is just an indication of how intense or difficult the exercise is to a person. Now, just a reminder that what may seem difficult to you, may actually be easy peasy to the next person, so exercise intensity is subjective. You could see that at 25%, which is an easy work out (like maybe a stroll in the park) and your heart rate is maybe only up to 75% of max, you burn mostly FAT and very little CARB. Note that this is in Percentage of total fuel source and not an absolute value. As intensity of the work out increases to 85%, which is maybe running for most people, and the heart rate goes up to about 80-90% of max, your body starts to switch to more CARB and less FAT burn. Because when we are working out that hard, the body wants energy FAST and EASILY available. Here’s another chart to put that into perspective.

So, how is this information useful? Ok. It depends on your goal.

Lose weight and tone up. You need to know that even though exercising at low heart rate intensities burn more fat than carbs, it is a percentage and in actual fact it only burns very little in absolute. For example, walking slowly for 30 minutes in the park may burn up to maybe 100 kcals in absolute total. Of this 100 kcals, 85% which is 85 kcals, were Fat fuels and the other 15% were carbohydrate fuels. But in absolute, you only burnt 100 kcals. When you go for a high intensity workout like a run for 30 minutes, you may burn up to maybe 300 kcals. Of this, 30% which is about 100 kcals, were from fat fuels and the rest were from carbohydrates. But in absolute you burnt 300 kcals and of which, 100 kcals of fat! See?

Gain muscle mass and get ripped. I think there are many out there who wants this. And many trainers out there will recommend you to up your protein intake and maybe cut out carbs. Not really the best idea, because when you cut out carbs, and you continue to train hard, what do you think is going to happen? Your body is going to run out of carbs and start eating up your proteins. Drinking protein shakes help in recovery i.e. building more blocks, but that isn’t really a fast process and your body can only handle so much protein at a period of time. The rest of it gets flushed down the toilet. So while you’re drinking protein and wasting away at least half of it, your body is continuously burning fuel because of your training. On top of this, you cut out carbs from your diet, so it has NO CHOICE but to start burning up protein!

My recommendation is for you to keep your carbohydrates, you may probably lessen the amount, but never completely cut them out. You can continue to drink your protein shakes but only if you plan on training hard frequently i.e. 5-7 times a week. And while you’re eating, just eat more organic sources of protein like eggs and meat which I think your body would prefer to use, rather than processed powder form protein. Just saying.

Hope this helps some of you! For more information you may want to read an article from or this one here from

2 Responses to Burn, Baby, Burn!

  1. Jaclyn

    Thanks this is soooo informative. I have been trying to lose weight and get back to my pre-pregnancy body but the last few kilos just don’t seem to bulge and i often feel tired and lethargic…….could it be because i have been cutting down carbs?

    • Karen

      Hi Jaclyn, thanks for your question!
      There is a saying about pregnancy, not sure if you have heard it before, it goes “9 months up, 9 months down”. Simply put, it took you 9 months to put on that weight, it’ll take you roughly 9 months to shake it off, gain your fitness back and go back to your pre-pregnancy body. How long ago did you deliver your baby?

      Yes, cutting down carbs will cause you to feel lethargic and tired. If you’re still breast feeding that will also use up a lot of energy and you get more tired. As long as you plan to exercise frequently, you should always have some carbs to fuel your exercise. Also, a lot depends on the type of exercises you do…very often an exercise routine becomes stale after a few months and your weight loss will reach a plateau. You will need to modify your exercise routine by increasing intensity or changing the movements so your body will start to burn again. =)

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