In a previous blog entitled how fat burning works, I set out what we mean by “fat burning”. Judging from the social media conversations the concept is still confusing. The cause of the confusion is mostly because of a mix-up of fat oxidation at rest or during exercise (which is what I called fat burning in my blog), with the capacity to oxidize fat. I used a factory analogy. If we use a similar analogy: fat oxidation (fat burning could be the production of the factory on a given day). That production may occur at a fraction of the capacity of production. Increasing the capacity is of course not something you do in one day. That takes weeks, months or years of hard work.
Why fat burning?
Now let's go back to the question: why is it that we want to burn fat? Why is this such a popular topic? And why does everyone believe that this is a good thing?
There is not one answer to this question because people want to burn fat for different reasons. The number 1 reason is probably losing weight. Weight gain after Christmas is usually gain of body fat and losing body fat would require burning the fat. Also athletes who already have a low body fat and want to get even leaner are often interested in fat burning for this reason.
Another reasons is that trained athletes typically have a higher capacity to burn fat. Weeks or months of training have changed the muscle and this now allows the athlete to burn fat a higher rates. This makes you less dependent on carbohydrate and thus you spare your glycogen (carbohydrate) stores and that should help your performance.
Fat burning is also linked to improvements in general health. This is mostly based on observations that if your body becomes very poor at burning fat (usually because of inactivity and a poor diet), people also seem to develop various metabolic and other health problems.
So if these are the 3 prime reasons of why we are interested in fat burning, let's have a quick look at the evidence.
Fat burning and weight loss
In order to lose weight we need to be in negative energy balance. In other words: you need to burn more calories than you ingest. If you burn more fat, but you eat more calories than the calories you burn in total, you will not lose weight. Of course when you are in negative energy balance, you want to make sure that the weight you are losing is mostly fat and this is where fat burning becomes more important. So the take home message here is: For weight loss negative energy balance is far more important than fat oxidation per se. Fat oxidation and weight loss are not synonymous.
Fat oxidation and weight loss are not synonymous.
Fat oxidation and performance
The second point was based on the premise that trained athletes are better at burning fat. In general this is true, but not always. What is true, is that any person can improve their capacity to burn fat through training and thus become better at burning fat. However, there are large individual differences and the starting points of different people can be very different. We don’t (yet) understand all the factors that cause these differences but it is very likely that they are largely genetically determined. In one study we found that some sedentary individuals were able to burn similar amounts of fat as a highly trained athlete. But as mentioned before everyone can increase his own capacity to burn fat, there is just no direct or linear relationship between fat oxidation and performance.
Training to increase fat burning capacity
If athletes want to increase the capacity to oxidize fat, there are many different training protocols to do this, ranging from prolonged endurance exercise to high intensity interval training. There is currently no evidence that one method is more effective than another. Most of these studies are a little removed from reality anyway because who would follow a training program with only one type of training (only long and slow or only HIIT).
There is currently no evidence that one method is more effective than another
Fat burning and health
The third reason to be interested in fat burning would be because it is linked with better health. Studies have shown that problems with fat oxidation and metabolic regulation in general are linked with health problems. Therefore it seems logical to assume that increases in fat oxidation are beneficial to health. Although I think in general this is a pretty strong argument it is important to note that we are talking about the capacity to oxidize fat more than fat oxidation per se. It is this increased capacity of the muscle to oxidize fat that results in benefits not fat oxidation per se. In most studies this increased capacity to oxidize fat was achieved by exercise. It difficult to separate the effects of fat oxidation from the overall effects of exercise. It is therefore almost impossible to attribute the benefits to an increased capacity to burn fat and not to the other benefits one would get with exercise.
So in conclusion, it seems that there is a lot of evidence indicating that an increased capacity to burn fat as a result of training is beneficial to both performance and health. The amount of fat you burn during exercise (or at rest) can be, but is not always a reflection of that. Fat oxidation is not equivalent to weight loss.