In continuation to the blog about fat burning physiology, I’ll discuss the transportation and then finally oxidation of fat molecules into energy. The process of fat burning is quite complex, but I’ll keep it as simple as I can….
As discussed in previous blog, in order to mobilise fats, we need to be In a Insulin/High glucagon sweet spot in conjunction with high levels of HSL. Once all these processes are in alignment mobilisation of the fat can occur. FFA (Free fatty acids) bind to a molecule called albumim and are then released into the bloodstream. The reason for this is that blood is water-based plasma and fat is NON water soluble so albumin interacts with the fat cells and acts as a carrier protein for the fats which allows them to be transported to the muscle cells where they will eventually undergo oxidation and conversation into useable cellular energy.
Once inside the muscle cell the fatty acid will either be oxidised to produce energy, only around 80% is used in total as energy, the remaining is stored in the muscle as the metabolically active fatty acid, intramyocellular triacylglycerol.
In order for the fatty acids to the oxidised they must first be transported by a protein called carnitine into the mitochondria. Once in the mitochondria, they then pass through several enzymatic pathways including beta-oxidation, tricarboxylic acid cycle (TCA), and the electron transport chain to create ATP for cellular use.
The oxidation step is more complicated than I’ve made it sound as there are several pathways FFA need to take once inside the mitochondria, but one of the most important aspects here is correlation between the levels of available carnitine (nitrogenous compound naturally found in human skeletal muscle, heart, liver, kidneys and blood plasma) and amount of FFA transported for energy use. Carnitine’s function is to facilitate the burning of fatty acids by enabling transport of long chain fatty acids into the mitochondria. If it is presents in low levels, we have a lower level of fat burning. The levels of carnitine in muscle is directly proportional to muscle glycogen stores, so to therefore fat burn we need to first decrease muscle glycogen which increases carnitine levels.
It's for this reason that fitness trackers can be a tad deceiving when it comes to what telling you where the energy for your workout has come from. You can open your tracker’s app after 50 minutes of exercise and see “fat burning zone: 45 minutes” but this is based purely from an estimate of heart rate during exercise. As I’ve just mentioned, it’s not as simple as it looks on the surface, your tracker doesn’t know your skeletal glycogen levels pre and post exercise, it doesn’t know what foods you’ve eaten and how this has affected your hormonal secretions (as I said in previous blog, if there are high levels of insulin, there this will affect the levels of HSL and therefore reduced fat burning) it’s based purely off a standardised equation comprised of your heart rate, age and current weight during exercise. Now, I’m not saying that all trackers should be disregarded, they can give a good overview of how much work has been done and a rough estimate of calories burnt, but do not think that because your watch tells you that you’re in a fat burning zone that workout is being fuelled entirely by fat.
HIIT is a popular workout choice because in a short period of time you can dramatically reduce levels of glycogen and force your body to pull energy from elsewhere. Of course, there are aspects to watch out for since your body does not just switch straight to fat once your glycogen has been depleted. Protein can also broken down for use as energy which is why pre/post exercise nutrition is such a huge part to weight loss/muscle retention. Steady state cardio has lost it's place to HIIT in recent years, you don't see many steady state cardio classes at gyms for the simple reason that they're time consuming and, in all honestly, can be a bit boring, but this doesn't mean that it is ineffective to fat loss...So never adhere to just one type of training, your body adapts to what your doing so if you want to keep the fat coming off then keep it varied and understand the role of nutrition in weight loss staying healthy in general.
Up next….Oxidation and energy release.
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