Which athlete does not want to be the "lean mean fighting machine"? Burning fat is often talked about as the road to becoming such a machine. Fat burning is a common topic of conversation amongst athletes and non-athletes.

Why fat burning?

In today's society, as a population, we are not burning enough fat (calories) and we are eating more fat (and more calories) than we burn. It is therefore not surprising that people are searching for ways to "burn more fat" (ideally ways that do not require too much effort).

Many companies have recognized the potential and have jumped on the opportunity and are now selling tools that help you monitor fat burning and supplements that supposedly increase fat burning. But do these things really work? Are there easy ways to increase fat burning? Are there easy ways to become lean?

Back to basics

Let’s go back to the basics and the simple facts first. Let’s looks at what the evidence says and what we really know. In a series of articles on mysportscience.com I want to evaluate the following:

1. What is fat burning? And how is it regulated in the body?

2. What are the main reasons why people/athletes want to burn fat?

3. What is the evidence for each of these reasons?

4. If we want to burn fat, what are the best methods to do this?

5. Can we come up with some general advice?

Let’s start with the very basics. Fat burning or fat oxidation (the term preferred by scientists) occurs on a daily basis in virtually all cells of our body.

Fat storage and use

Fat is stored in the form of triglycerides. A triglyceride is made up of 3 fatty acids that are held together by a glycerol backbone (hence the name tri-glyceride). Only fatty acids can be used as a fuel. Therefore triglycerides first need to be broken down into fatty acids. The fatty acids then need to be broken down further.

How do we oxidise fat?

Fat oxidation refers to the process of breaking down fatty acids. To oxidize fat one needs:

1. Healthy mitochondria (small structures in cells that serve as the power plants of the cells. In these power plants, energy is generated for muscle contraction by burning fuel, using oxygen and producing carbon dioxide).

2. Supply of fatty acids (these are supplied from triglycerides and fatty acids in the blood, as well as triglycerides stored in the muscle itself)

3. Oxygen (transported to the muscle by blood)

If fatty acids are supplied to healthy mitochondria and oxygen is present, fatty acids will be broken down to carbon dioxide. This process is not too dissimilar form burning a log in a fire. You need the fireplace, some wood and oxygen.

The process of fat burning has several components

As mentioned above, the fatty acids we burn can come from different sources. Fat is stored as triglycerides in different tissues of the body, including muscle. The vast majority of triglycerides in our bodies can be found in fat cells. When we eat, fat will eventually appear in the blood stream and can potentially be taken up and used in the muscle. When we exercise, our need for energy increases dramatically because muscle contraction is an energy consuming process. Some of this energy will come from fat burning.

Fat burning in the muscle depends on

1. The availability of fat in the muscle

2. The enzymes in the muscle to break down triglycerides to fatty acids

3. The enzymes in the fat tissue elsewhere in the body to break down triglycerides to fatty acids

4. The supply of blood to the muscle

5. The presence of transport proteins to carry fatty acids from the blood into the muscle

6. The efficiency of transport of fatty acids into the mitochondria (we will discuss this in more detail in future blogs)

7. The number of mitochondria

8. The quality of the mitochondria and the enzymes in the mitochondria to break down fatty acids.

The factory analogy

Because there are so many steps, there are also many regulatory mechanisms. For example, the activity of the enzymes that break down fat (triglycerides) into fatty acids is regulated. Blood supply to the muscle is regulated as well as the uptake of fatty acids into the muscle and into the mitochondria.

Compare this process to a factory. The factory produces goods (energy). For these goods to be produced we need raw materials (fatty acids and oxygen). We also need machinery (mitochondria) and personnel (enzymes). There also needs to be a steady supply chain (trucks that bring in the raw materials) and it is important to remove any waste products (CO2) or use them for recycling purposes.

With this analogy it is easier to understand that simply giving one of the workers in the factory more tools, will not automatically mean that the factory can produce more goods and will not mean that is uses more raw materials. Similarly, ingesting a “fat burning supplement” that has a link to fat metabolism, does not necessarily mean that it will stimulate fat burning.

What will really improve productivity is if you could build more factories, with more machines, more personnel and improved delivery of raw materials. This is what training does. By training you generate more mitochondria, more enzymes, more transport proteins, better blood supply to the muscle and faster breakdown of triglycerides into fatty acids. The end result is a greater capacity to burn fat.

Take home messages

So although this is a very basic explanation of what we mean by “fat oxidation”, there are a few of important take home messages:

1. Fat oxidation is regulated at many levels and by many processes

2. It is therefore unlikely that a single intervention will significantly increase fat oxidation in a healthy person (it may be different if there is something broken in the factory)

3. Training is a very effective way to increase the capacity of fat oxidation although this of course does not happen overnight.

So now the basics are covered in future articles we can dive a little deeper and discuss the remaining questions about fat metabolism on mysportscience.com.