Why Does the Body Burn Muscle Instead of Fat?

Many ‘dieters’ or people aiming to shed fat experience muscle loss. This is somewhat an inevitable process (simply due to how our hormones respond to changes in diet and exercise) but the severity in which muscle is ‘lost’ can be controlled.

I eat fairly low carb diet so shouldn’t I be losing more fat? 

Firstly, if you are trying to shed excess fat you are exercising daily thus, you should not be on a “low-carb” diet. Presumably you are are exercising at a moderate to high intensity to maximize the number of calories burned.

Carbohydrates will be the  first source of fuel to be broken down into glucose to provide energy for your cells during the workout. After that first line of energy source is depleted (also known as glycogen), the body will look for the next most readily available source for energy to provide fuel for your workout. An obvious choice would be to attack adipose stores (fat cells) for stored energy (triglycerides) to convert into usable energy (glucose). This could be a plausible occurrence however, during higher intensity workouts (70-85% of max) and a depleted glycogen reserve, insulin levels drop significantly low and lactate levels have risen higher. What does this mean?

The rise in lactate decreases the rate at which triglycerides are broken down into free fatty acids and glycerol (usable form of energy). But… the body still needs the energy for your workout.

Ideally if Carbohydrates were available the body could breakdown glycogen into glucose to be used as energy. However, this person is on a lower-carb diet and is exercising, the body is in a negative energy balance and needs to provide energy in a usable form fast!

The body cannot be selective in it’s needs. It needs to produce glucose, not only for the brain (our brains uses up 20% of  glucose to function) but also for working muscles s0 – it goes to town on the other source of stored energy in our bodies – Protein.

The  usable form of energy derived from protein is amino acids. Our bodies have 3 sources of amino acids:

1) That obtained from dietary protein

2) free floating amino acids

3) muscle.

Unfortunately, we have brought our bodies to this starvation response -and 2 things have occured. One, as I mentioned earlier – Insulin levels have dropped. The prolonged drop of insulin levels elicits a stress response (see here for previous article on how Stress Makes You Fat). The stress response leads to a release of glucagon (to raise blood sugar levels) and ther glucocorticoids such as Cortisol. These hormones have a catabolic effect on body tissue and quickly breakdown muscle tissue to raise blood glucose levels (usable energy for the brain and working muscles).

Unfortunately the first 2 sources of protein (above) are used up very quickly and don’t provide enough energy (perhaps 5% of what is needed). So now, not only is the cortisol having a catabolic effect on muslce tissue, but muscle tissue is now the next in sequence to breakdown for energy. This has 2 problems:

1) Protein is not meant to be a primary source of energy hence the yield of energy it produces is also small.

What does this mean? Unfortunately quite a bit of protein needs to be broken down to produce energy. Hence there is a small bang that come at a large cost. Let me say that another way – a lot of muscle needs to be broken down to produce minimal energy.

2) For the person that is aiming to shed fat: Muscle is lean mass and essentially increases your fat burning potential. By bringing yourself to this negative energy balance, the body is forced to use muscle protein for fuel hence you are decreasing your fat burning potential.

So what to do?

The likliehood that you can completely avoid even the slightest muscle protein breakdown is slim simply due to the fact that exercise increases protein degradation (breakdown) and decreases protein synthesis (building). But exercise also increases Growth Hormone (GH) which combined with the right calories and proper nutrition – increases protein synthesis. Having a nutrition plan that is correct for you is important to making sure you are experiencing positive results from your workout and to minimize muscle breakdown.

Fuelling properly pre workout is also extremely important.

For example: Almond Butter (fat) on toast (catb) with a side of Greek yogurt (protein) and a handful of berries (carb)


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Filed under Get Leaner and Stronger, Stress & Stress Management

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