Fat Oxidation and Fat Loss, The Whole Picture
A large portion of the fitness world absolutely LOVE talking about fat burning. Supplement companies take huge advantage of this “THIS FAT BURNING SUPPLEMENT WILL LEAVE YOU LOOKING LEAN AFTER JUST 2 MINUTES OF TAKING IT!”. “I SHOVED THIS PILL UP MY BUTT AND IT BURNT OFF ALL MY FAT”
You get the idea. There are a lot of claims out there around fat burning and unfortunately it means that it’s fairly common to be confused about fat burning and what’s actually going on! So here we’re going to dive into what fat “burning” or oxidation actually is, how this relates to fat loss and then dive into the actual whys and whats about increasing fat oxidation!
Now it wouldn't be a fat burning blog if we didn’t talk about one of the most polarising diets out there, the ketogenic diet (Very high fat, less than 50g Carb).
Now before we dive into it, it’s worth me saying that I have absolutely nothing against the ketogenic diet and there is a small body of evidence that shows the ketogenic diet may have very useful applications in the treatment of epilepsy. For most people though it’s likely a relatively unsustainable diet choice.
Sweet, now that’s out of the way let’s look at it in the context of fat burning.
Fat Burning / Fat Loss
People on the ketogenic diet often make the claim that they are burning loads of fat! This is without a doubt a very true claim to make, however they often mean in the context of their fat stores, which isn’t necessarily true. The amount of fat that a person loses is dependent on the amount of fat they deposit, and the amount of fat that they oxidise “burn”. In the context of the ketogenic diet, they take in a significant amount of fat and if they’re eating at maintenance it’s likely that the amount of fat they are storing is around the same as the amount of fat they’re oxidising.
And when Fat stored=Fat oxidised we see no fat loss.
On the flip side, if we were to look at a low fat high carb diet it’s likely that fat oxidation is low, carbs will be the predominant energy source! But again, if calories are at maintenance the amount of fat being stored is likely going to be equal to the small amount being burnt. Fat oxidation=Fat Stored we see no gain in fat!
Turns out our old friend energy balance is the driver behind fat loss and fat gain! This has been shown time and time again in many studies. When calories and protein intake is matched, there doesn’t seem to be an advantage to a low carb or low-fat diet when it comes to fat loss.
Of course, whichever one you can adhere to is the best and which will help with your training is key too.
The Fat Burning Zone
So that’s fat burning in the context of body composition, but we also hear it talked about in other aspects of nutrition and performance. For example, several heart rate monitors have a recommended “fat burning zone” and there’s even an entire principle in performance nutrition (train low, compete high) dedicated towards increasing fat oxidation at certain stages of training!
Well this is based on the idea of metabolic flexibility, the capacity to use one substrate or another depending on the demands of the exercise you’re carrying out.
Fats and carbs are our bodies largest stores of energy and at higher intensities we use more carbohydrates than fats! We are more able to oxidise fats at lower intensities as we are pulling in more oxygen (clues in the name, oxidising).
The idea is that if we can become more efficient at using fats at low intensities then we can spare our carb stores for when we really need them.
Thus spawned the train low compete high principle. It is based on the idea of periodically training in a state of reduced carb availability but competing in a state of high carb availability, which allows the best of both worlds when it comes to our fat and carb fuel tanks. This is where the idea of training in a fat burning zone is useful as training can match the nutrition to force the desired adaptation.
So it does have some usefulness! BUT how do we know if we are burning fats?! Well the heart rate zones that a Polar or Garmin may give you are estimations based on percentages of your maximum heart rate, but these may not be accurate. The way that we clinically measure fat oxidation is through gas analysis and a metric called the respiratory quotient (RQ) or respiratory exchange ratio (RER).
The RQ is defined as the volume of carbon dioxide released divided by the volume of oxygen absorbed during respiration. It is usually a value between 0.7 and 1. The closer it is to 1, the more carbon dioxide is being produced which tells us more carbs are being used as a fuel.
Above 1 anaerobic respiration is the predominant driver for energy production. The closer it is to 0.7, the more fats are being used. A value below 0.7 may indicate ketones becoming a fuel source.
Tests can be carried out to find the intensity and heart rate at which fat oxidation is highest.
Here’s an example graph taken from Asker Jeukendrup to show the change in fat oxidation as exercise intensity increases.
We can see that there is a peak or a “FatMax” that shows the point of maximal fat oxidation. This can be used to guide training for those reduced carb availability sessions.
Round Up
So there we have it, the truth about fat burning, it’s impact on body composition and when it’s actually useful! Keep an eye out for an incoming blog all about training low for more info on that!
In the meantime if you’re keen to get your fat max tested then drop us a line and book in a test soon!
Performance Nutrition In London
Looking to optimise your performance and understand how better to fuel yourself? I’m a performance nutritionist with a Masters in Human Nutrition that has helped countless athletes improve their performance. Head here to see what we offer.
