“Fat burning” is a popular term in fitness. You see it a lot in commercial gyms, it’s a relative buzz word for getting people’s attention getting them into a “I can just do this and be skinny mindset”.
Come see our new “fat burning” workouts and/or diet plan, HIIT sessions or pill/supplements. It’s an easy term to throw around knowing how it works. ANYONE can label something as fat burning. Sitting about can technically be fat burning (around 50% of our energy at rest comes from fat). But the first thing you need to realise is we cannot pick and choose where we get our energy from, out bodies do that for us. Our energy comes from biochemical reduction of a molecule called ATP which creates energy that drives almost every process in the human body. But we have finite concentrations of ATP, so once the go to fuel of glycogen is depleted, our body then turns to “Fat burning”. From a biochemical perspective, fat undergoes oxidation of into usable fuel, but again, you can’t just tell your body to burn fat because you want it too. Initially during bouts of exercise, the process of glycogenolysis first converts glycogen that’s stored in the liver into glucose which in turn is released into the bloodstream to deal with low blood glucose. Now, when the stores become depleted, as a safety mechanism the body looks for fuel elsewhere, this is where the breakdown of non-carbohydrate substrates comes into play….Naminly, proteins and fats.
So it’s not as simple as “pop a fat burning supplement” or simply labelling a clients workout as “fat burning”. What fuel source your body uses is heavily determined by presence of glycogen within the body, intensity of workout and duration of workout.
Now, there are three stages of burning fat that I will cover over three different blogs:
This week: Mobilisation
The process of mobilisation means that the triglycerides (stored fat) in the fat cell (adipocyte) must been broken down through a process called lipolysis, once this has occurred, it can then enter the blood stream for transportation. This is the first stage towards oxidation and conversion to a useable fuel source.
But let’s go into a bit more detail, the fat inside the adipocyte is mostly in the form of triacylglycerol (known as TAG or triglycerides). When it’s required, the TAGs are broken down (lipolysis) into diacylglycerol (DAG) or free fatty acids (FFA) and glycerol. This leaves one molecule of glycerol and three molecules of fatty acids. It’s important to note that not all the fatty acids that are mobilised are oxidised as fuel, some of the fatty acids from lipolysis are re-esterified to triglycerides.
Metabolic Hormones and Fat loss
Here’s where my previous blogs come into play, to mobilise fat, the body needs to be in a hypo caloric state in order for the body to signal to draw it from stored non-carbohydrate stores such as fats and proteins. This doesn’t mean you HAVE to eat less, you either need to be in a caloric deficit or have an increased energy output (so if you consume 2000 cals, and your BMR is 1600, you would need to burn 500 cals). If in a caloric deficit or intense exercise bout the concentration of glucose in the bloodstream drops therefore insulin levels lower and stimulates secretion of both glucagon, hormone sensitive lipase (HSL) and catecholamines. (see previous blogs about metabolic hormones).
The metabolic hormones Insulin and glucagon are responsible for management and regulation of blood glucose always. The process can be simplified: eat and/or have excess energy and the pancreas releases the hormone insulin to move glucose from the blood and into cells for energy or storage, if this doesn’t happen, the complication is called diabetes. At this stage it also serves to keep HSL low to limit fat mobilisation and keep the fatty acids inside the cell. It does this because fat is important, it’s a reserve as well as serves numerous functions in our bodies. For this reason, we class Insulin as an anti-lipolytic hormone
Hormone sensitive lipase (HSL) is possibly the most important enzyme in the regulation of stored fats (lipids). If HSL is low occurring at a reduced/low rate, then fat mobilisation will be slow, if HSL is high then fat mobilisation will be fast. So a rise in Insulin secretion causes to HSL to decrease.
If fat reduction is a client’s goal, then eating carbohydrates prior to a workout will actually increase insulin, lower glucagon and decrease both glycogenolysis and gluconeogenesis. When cellular and blood glucose are low, glucagon rises promoting both gluconeogenesis and glycogenolysis. The main hormones that activate HSL are the catecholamines, epinephrine (adrenaline) and Norepinephrine (Noradrenaline).
Catecholamines like Epinephrine binds to the adipocyte and causes hydrolysis of the TAG into glycerol and free fatty acids (FFA) allowing it to enter the blood stream.
So, in order to mobilise fats, we need: Low Insulin/High glucagon, high HSL (process is limited by high insulin and high blood glucose), high catecholamines secretion (these need low blood glucose levels and/or intense exercise, the more intense the higher catecholamines get which is why HIIT is a popular method for fat loss clients).
Next time, Fat Transportation.
Our Recent Posts
Age old question and probably one of the main reasons people abandon their diet and workout routines. Trying to explain to people that weight loss SHO...
How Often Should You Measurements To Track Progress?
September 9, 2019
Just a reminder, calorie calculators and CICO aren’t the same.
Whilst many people use calorie calculators to estimate their energy needs and adjust the...
Calorie calculators - cals in vs out aren’t the same
August 2, 2019
This is probably one of the weirdest issues in the fitness industry to date. I've seen trainers post massive facebook/insta blurbs and charge clients...