Building muscle and burning fat – is it possible?
In Part 1 I explained the process of burning fat and fat synthesis. Today, let’s answer the question: Does exercise increase fat loss?
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Primary sources of energy during exercise
The primary source of fuel during exercise is carbohydrates.
In comparison to protein and fat, they are easy to break down and don’t burn as many calories. Carbohydrates stored in our muscles and liver are the first to be used during exercise lasting between 1-20 minutes.
It does not take long until the stored glycogen is all used up, especially if exercise intensity is high. Thus, the body needs to begin using fat as fuel to get ATP (energy equivalent in our body).
Protein is not used as fuel during exercise, as it takes too long to break down and burns many calories as well. The only exception is if you have been starving and your body does not have enough stored glycogen or free fatty acids to use as fuel. This is why I don’t recommend training fasted!
Exercise: Effects on fat loss
How exercise effects fat oxidation in a 24h period is a topic that is still not researched thoroughly. However, studies have shown that individuals with reduced rates of fat oxidation tend to gain weight more easily. Furthermore, obese and insulin resistant individuals seem to have a decreased capacity to oxidize fatty acids.
What are the acute effects of exercise on fat metabolism?
The effect of exercise on oxidation of the different types of fat (depending on the length of the fatty acids chain) has been well studied. It has been shown that the primary source of fatty acids in skeletal muscle during exercise are long-chain fatty acids (those our body cannot produce on itself to an extend), especially during long-duration low-intensity exercises.
The metabolism of low-density Triglycerides (also called VLDL-TG) is regulated by an enzyme called LPL (Lipoprotein lipase). This enzyme is not very active during moderate intense workouts but increases markedly following exhaustive and/or glycogen depleting exercise. As a result, triglycerides in our body are burned to a higher extend with short bouts of exhaustive exercise, also called “high intensity training” (HIIT).
As I explained in the first part of this series, VLDL-TG is exactly the kind of fat we want to be burning, to reduce risk of obesity, diabetes and many other diseases.
However, the rate of fat burning depends on the transport system in our mitochondria. If your body lacks Carnitine, it will not be as efficient in fat burning because the fatty acids cannot reach the place where fat oxidation occurs.
Endurance exercise increases the density of our mitochondria, activates more enzymes and leads to higher rates of fat oxidation in general.
In addition to that, it has been shown that training (in general) increases activity of LPL. As I explained above, this enzyme is important for VLDL-TG metabolism and helps to burn off the unhealthy kind of fat.
In contrast, fat oxidation is not higher in trained individuals than in untrained ones. While we rest, our metabolism returns to its normal state. However, during exercise, trained individuals are able to burn off more fat because of higher density of mitochondria and more LPL.
About the fat burning zone
It has been shown that low intensity exercise is not very efficient at burning fat. However, some studies suggest that very exhaustive exercise might decrease fat oxidation (especially if it is long duration). The reason for this is the decrease of blood flow to our adipose tissue, which leads to less free fatty acids available to burn. This is a topic that is still not very well researched though.
Interestingly, women seem to be more efficient at burning fat as well. This may be due to different hormone levels and catecholamines in their body. As I explained in the first part, catecholamines increase fat oxidation (lipolysis).
Still, to answer the question of the “perfect fat burning zone”:
Several studies have been made and the results were pretty similar: The rate of VO2 max, at which people burned the highest amount of fat, was completely different for each individual. We cannot state that low-moderate intensity exercise burns the highest amount of fat. The “fat burning zone” is therefore a myth and cannot be scientifically proven.
However, we can state that maximal fat oxidation rates are higher in trained individuals and increase as intensity does. Thus, obese people are not as efficient at burning fat as trained individuals were.
In conclusion, exercise increases the capacity of muscle for fat oxidation. The more trained you are, the more fat you can utilize for energy.
Exercise and the “after burn”
The same study examined not only the acute effects of exercise on fat oxidation but also its effect on fat burn up to 24h after training was completed.
The results were pretty interesting:
Whether exercise alone increases fat oxidation depends on nutrition! The individuals in the study all trained in a fasted state and their macronutrient intake was less than energy outtake. Thus, they were in a “fat balance” / macronutrient balance. After the training session, they had a higher rate of fat oxidation for hours.
However, individuals that had around 60g of carbohydrates before the training session did not experience this effect. If you remember, I explained in the first part that Insulin decreases lipolysis. If we consume carbohydrates before exercise, Insulin is released and will inhibit lipolysis. This is great for anyone who wants to build muscle, as Insulin also increases protein synthesis.
In the study, the individuals who were not in a macronutrient balance did not experience the so-called “after burn effect” of exercise, thus increased fat oxidation did not occur.
We can conclude that using exercise for fat loss is not as efficient as nutrition. Exercise increases the muscles capacity to burn fat but without the right diet, it is not effective.
So, the conclusion of today’s findings is:
Don’t see exercise as a tool to burn fat. Exercise is your weapon against injuries and diseases, it will make you stronger, healthier, improve your mood and help you live longer. However, if you want to lose fat and think that exercising alone is sufficient, you are fooling yourself.
In fact, you can lose fat without exercising at all!
As you can see, processes in our body are very complex. It is easy to state “this and that is the perfect fat burning zone”, or “do this workout to burn tons of fat!”. I might be wrong, but I think that exercising is far more convenient than changing eating habits. Exercise takes only 1 hour of our day but how you spend the other 23 hours in the kitchen is what will bring you the best results.
Does it make sense to work out at all to “burn fat”, if exercise is not as efficient as nutrition at fat oxidation?
Yes, of course it is! I don’t want you to neglect exercise. If you have a lot of weight to lose, are Insulin resistant, have diabetes, suffer from an autoimmune disease, cancer, heart disease … exercise is your best weapon to fight back!
Even if your goal is solely fat loss, you should always look at the big picture.
It is not about what you look like, but about what your body can do!
Shift your focus from fat loss.
Have fun with your workouts and find goals you want to achieve that include strength or cardiovascular fitness. It is great to have lean legs but I assure you, being able to finish a 30 min HIIT session without taking any breaks will leave you much more accomplished!
The next part is going to examine the effects of nutrition on fat loss. Stay tunes to find out how to really increase fat oxidation!