The first fuel tank of energy for your body is your blood sugar. It is a combination of proteins, carbohydrates and dietary fats (not body fat) put into the bloodstream shortly after eating, through the digestion process. When food is digested the energy stored in the food is converted into sugars which are distributed into the blood stream, the muscles and the liver, and once those storage depots are replenished, in the fat cells.

Once that first fuel source is used up it then uses the energy in muscle tissue that is not used. Now why would the body cannibalize its own muscle tissue?

Remember that the body's only concern is survival. Muscle tissue uses more energy just being there. So if you have muscle tissue that's not being used the body considers it unnecessary and wants to get rid of it. Lazy muscle is free-loading off the rest of the body. (It's like leaving lights on in the rooms of your house when you aren't using the room... A waste of energy.)

So unused muscle tissue is broken down and used up as fuel. This is why people lose lean muscle tissue when they go on starvation diets. You'll also see this in the atrophy (withering away) of muscles which are not used such as when a limb is immobilized. Less muscle means less energy is used by the body overall.

(I guess the lesson here is: Use it or lose it. Don't let any muscles just lie around. Move your body in all its ranges of motion as much as possible.)

Once excess muscle tissue is eaten up the body then uses the muscle energy glycogen that is actually stored in the muscles. Muscle glycogen will only be used up before actual muscle tissue when sudden intense stress is loaded upon the muscle.

This energy (glycogen) is used primarily for sudden intense workload placed upon the muscle. It is the fuel for hard physical labour, intense aerobic bursts or heavy weight training.

Note that it is not called upon for light to moderate activity. So once your blood sugar is used up, light to moderate activity breaks down unused muscle tissue rather than using the glycogen stored in the muscle. This is why it is important to engage in short burst intense aerobic activity like intervals or circuits or use weight bearing exercise.

Don't think that just doing long walks (moderate activity) will burn up all your fat.

Also, don't think that weight bearing exercise will always use your muscle glycogen stores. If the weights are too light and you are just 'going through the motions' the load imposed on the muscle may not be enough to activate the glycogen burning process.

If the body has used up the fuel in all those energy sources:

oBlood sugar

oMuscle tissue

oMuscle glycogen

Then it will mobilize its fat stores as energy and begin to consume body fat.

But this is a big ask because by this time you have probably eaten again and replenished your blood sugar supplies. This means the fat stores are often hardly touched. If you haven't eaten and your body needs fuel for its current activity level then it will consume the body fat for energy.

This is a good reason for doing your exercise after getting up in the morning. As long as you're doing the right intensity of exercise your blood sugar and muscle glycogen is quickly consumed and you can get into your body fat to keep you going. But it doesn't mean you should starve to make your body consume its fat reserves.

Compounding this difficulty with burning fat is the body's natural mechanism to slow down the metabolism when few calories are being ingested.

It automatically slows down the metabolism to conserve fuel by burning less fuel.

So reducing food intake sends the body into ‘survival' mode against starvation and actually makes fat loss even harder.

See why it is so difficult shedding your excess fat?

Now that you know how your body uses up its energy you will be able to do the right things in the right way to more effectively reduce body fat.