To lose weight — and keep it off — it’s critical to understand how fat loss happens in your body.
To help you optimise your fat loss journey, this article will teach you everything you need to know about oxidative priority (the order in which you tend to burn the fuels available to your body).
Unfortunately, because your body loves to store it, your body fat is last in line to be used. However, by intelligently managing the upstream fuels — like carbs, fat and alcohol — and giving your body what it needs, you can ensure your unwanted body fat is used sooner rather than later.
What is Oxidative Priority?
Imagine if you poured crude oil on the ground, poured petrol on top and lit a match (please only imagine; don’t try this at home!). The petrol would burn off quickly, and the oil may not even ignite. Oil burns slowly, while petrol burns quickly.
Volatile fuels like gas are hard to store. In contrast, it’s much easier to store large amounts of energy as unrefined crude oil. In addition, the more we refine these fuels, the faster they burn.
In a similar way, the foods you eat behave differently in your body depending on their degree of processing and their macronutrient profile.
The fact that different macronutrients are harder to convert, and there are more significant losses in their conversion, is a highly underappreciated food parameter that goes by several names, including:
The Order Your Body Uses the Food You Eat
The food we eat contains macronutrients that behave uniquely in your body.
Alcohol is a volatile fuel that we can’t store. So, your body works hard to use it first.
Your appetite for high-protein foods also shuts down once you’ve had enough.
Carbohydrates and fat
While your body likes to maintain some glucose in your bloodstream, you won’t burn the fat in your blood if you have too much glucose floating around.
A little dietary carbohydrate can quickly raise your blood sugar levels because you can only store about 5 g of glucose in your blood (about a teaspoon’s worth).
While we can convert dietary sugar into body fat through a process known as de-novo- lipogenesis, it’s usually dietary fat that is stored as body fat, because our body prioritises burning glucose first and fat last. Thus, dietary fat that is not immediately burned off is easily stored.
It’s not necessarily that fat is a better fuel source than carbs, but rather that glucose will show up in your bloodstream and register on your blood glucose meter after you eat. Glucose essentially ‘floats on top’ of the fat in your bloodstream and adipose tissue.
But it’s critical to note that the rise in blood glucose is also influenced by the fat in your diet and the fat stored in your body. If your fat stores are already full, additional carbohydrates will affect your blood glucose much more. Achieving healthy blood sugars is not simply a matter of avoiding carbohydrates. Instead, you need to reduce the total amount of energy stored in your body so the glucose doesn’t back up into your blood.
While we always burn a mixture of available fuels, the body prioritises the oxidation of the more volatile ones first. So, to access your body fat, you must deplete any excess glucose and fat in your blood first.
Your Body’s Fuel Tanks
In your body, your fuel tanks for glucose and fat are separate but somewhat interconnected.
As you deplete your blood glucose, the glycogen in your liver will be used to refill it (note: glycogen is the fancy name for the storage form of glucose).
Only once you start to draw down glycogen stores in your liver your body will turn to the fat in your blood before moving on to using your body fat for energy.
You can think of your available fuels like Jenga blocks stacked on top of one another, as shown below. When you measure blood glucose, you are not just measuring the sugar in your blood. Instead, you measure all the fuels cumulatively stacked up in your body.
|glycogen in liver and muscle|
|free fatty acids in your blood|
If you want to nerd out a little more, the following table shows more detail in terms of:
- oxidative priority,
- approximate capacity to store the various fuels, and
- their thermic effect.
|Alcohol||Ketones||Excess Protein||Glucose||Fatty Acids||Body Fat|
|Use||Energy||Energy||Energy & Excretion||Energy||Energy||Storage|
|Capacity (calories)||20||20||–||1200 – 2000||150||40,000 – 500,000|
|Thermic effect||15%||3%||20 – 35%||5 – 15%||3 – 15%||3 – 15%|
How Your Body Uses Available Fuels
Oxidative priority helps you understand how the different fuels you’re consuming are used and stored. Before we dive into how you can measure and manage your various fuel tanks, let’s quickly look at how your body uses the food you eat.
Alcohol and Ketones
You have limited capacity to store alcohol or ketones in your blood.
Because they are more volatile than the other fuels, they are the highest priority to be used. Interestingly, alcoholics tend to have very low HbA1Cs. This oddity is explained by oxidative priority. They must use alcohol before metabolising glucose, so your body holds back the glucose in storage in your liver until the alcohol is cleared from your blood.
Note: Ketones are usually only available when glucose and other fuels are very low, so this is not an issue. But if you are using exogenous ketones, keep in mind that they are just another fuel that needs to be used before glucose and fat.
Most of the protein you eat is used for muscle protein synthesis (MPS) and other critical bodily functions.
While ‘excess protein’ not used in MPS can be converted to energy (ATP), this is a labour-intensive process that usually only happens when you’re not eating enough carbs or fat to supply your energy demand. In this instance, your body turns to dietary protein and then the protein on your body (i.e. your muscles and organs) to provide itself with amino acids and energy.
Excess protein, or protein beyond what is required for muscle repair and other bodily functions, is metabolised by the liver as urea and excreted in the urine. In other words, it is not used for energy.
Protein has the highest thermic effect of any other macronutrient, meaning your body has to work hard to convert it to usable energy. We expend between 20 to 35% of the energy we’re consuming when we turn it into usable fuel (ATP) and muscle.
Thus, we don’t usually consume ‘excess protein’ and tend to gravitate energy from fat or carbs once we get enough protein.
Your body has some capacity to store glucose in the blood, liver, and muscle. However, it’s not much compared to the amount of energy your body fat can hold! If you don’t consume many carbohydrates, your body will work to convert protein to glucose (through gluconeogenesis) to keep your glycogen stores topped up, so you always have enough glucose available when required.
Fatty Acids in the Blood
You have some fatty acids in your bloodstream to use for fuel. However, this capacity is limited compared to the space you have to store excess energy you do not use.
Because of genetics and other factors, some people can hold a tremendous amount of fat in their adipose tissue before it backs up and overflows into their bloodstream.
Meanwhile, other people’s fat cells have a smaller capacity to store fat before energy overflows into their bloodstream, developing diabetes. This difference in fat storage capacity is known as Your Personal Fat Threshold.
The bottom line is that you must deplete upstream fuels before your body uses any unwanted belly and bum fat.
What Does This Mean in Practice?
Imagine you’re at a BBQ, eating a burger with a beer and fries. These magical food combinations taste terrific, and we can eat a LOT of them because they allow us to fill all our fuel tanks at once (i.e. alcohol, carbs, and fat with a dash of protein).
This sort of meal would be perfect for a starving caveman or a marathon runner at the end of the event to quickly replenish depleted fuel stores. However, if you didn’t need that much energy, your body will spend a lot of time burning off the energy from this meal. First, the alcohol, followed by the carbs, and finally the fat.
Your glucose and insulin will be elevated for many hours as your body works to metabolise and store the energy. But if you eat again before you’ve used all of the energy, it’s primarily the fat that will be stored on your body for the long term.
In addition, these magical fat+carb combo meals that tend to raise our blood sugar and insulin for a long time, also often result in blood glucose crashes that leave us feeling light-headed, hungry and highly motivated to eat anything and everything, well before we used up all the energy from our last meal.
To put what we have learned about oxidative priority into practice, we can look at how a few popular ways of eating fill up your fuel tanks.
Scenario 1: A Modern Processed Diet
To unpack what oxidative priority means in practical terms, we have created some diagrams to help you visualise how you can unlock each fuel tank and burn body fat.
The body has four main storage compartments for energy:
- blood glucose,
- liver and muscle glycogen,
- fatty acids in the blood, and
- body fat.
The image below shows that these storage containers are separate but somewhat interconnected.
When it comes to oxidative priority, you can think of energy utilisation from left to right. If one of the downstream storage containers becomes overfull, energy flows back upstream due to excess pressure in other fuel tanks.
This first fuel tank is the glucose in your blood. Next, you have glucose in your liver and muscles, which is in its storage form, glycogen. Once you use these up, you must burn the fat in your blood and liver before moving onto your body fat.
These ‘tanks’ are separate but all connected by a ‘pipe’. The pipe connecting each fuel tank to the next flows downstream and towards the right.
Also, note that the pipe is not drawn to the bottom of each tank. You needn’t exhaust or empty each tank to access the next fuel. Instead, you must empty each one to normal healthy levels.
Unfortunately, we have optimised our modern diet to constantly top up every fuel tank at the same time. Eventually, all the fuels in your body become backed up, preventing you from ever calling on your body fat for energy.
Like the burger and fries with a beer on the side, when we eat hyper-palatable foods with a negligible nutrient density, we continue to fill our fat and glucose stores simultaneously.
Unfortunately, not only do these foods fill all our fuel tanks at the same time, but they also give us a double-dopamine hit, making it hard to put on the brakes once we start eating them.
When these foods are readily available, we have no off switch for them, and our storage tanks become overfull. Before long, we end up with energy toxicity, metabolic syndrome, diabetes, and other related conditions.
Scenario 2: Low-Carb Diets & Fasting
The good news is that we can start draining our glucose stores when we reduce carbohydrates.
But even if you go sans carbs, your body will refill your blood sugar from your liver glycogen stores, especially if you continue to overdo the dietary fat. This is why your blood glucose drops to zero and might even continue to rise when you don’t eat.
Your blood glucose is a small fuel tank that holds about 5 g or 20 calories worth of glucose. Thus, it fills and empties quickly before and after meals.
You can get a precise understanding of your current energy status by measuring your blood glucose with a glucometer. Our blood glucose gives us an accurate sense of whether our downstream fuel tanks are also overfilled.
In Data-Driven Fasting, we simply measure blood glucose before meals. This trains people to wait until their blood sugar drops below their personal blood sugar trigger point, so they can drain their glucose stores before they eat again.
Waiting until blood glucose drops stops people from overfilling their upstream fuel tanks. This, in turn, causes the body to use liver and muscle glycogen to refill blood glucose and deplete fatty acids in the blood, which are replenished from body fat stores. After you’ve given it a bit of time, voila! You’ll have lost body fat.
Some people run into trouble when they refeed with very high-fat foods. High-fat foods provide a low satiety value across the board, and fat is the most energy-dense macronutrient. This means that we tend to consume more calories when a high percentage of our energy comes from fat.
A keto or high-fat diet itself does not necessarily burn calories unless you’re also in an energy deficit. Per the First Law of Thermodynamics, energy cannot be created nor destroyed, and calories are still calories. Thus, if we eat a ton of high-fat foods and are not conscious of calories, our blood’s fat fuel tank is always topped up from dietary fat. Hence, there is little opportunity for body fat to flow back into the bloodstream and be used for fuel.
The idea that fat is a ‘free fuel’ because it doesn’t raise insulin over the short term is a mistaken belief. We have seen this in many Data-Driven Fasting participants who have very low and stable blood sugars but still carry a lot of body fat. So while their blood sugars are low, they continue to refill their fat tank, which keeps them energy toxic!
For more on this, check out Keto Lie #8: Insulin Toxicity is Enemy #1.
When people get stuck at this point, we recommend they focus on increasing the percentage of protein in their diet (i.e., by reducing both dietary carbs and fat). This improves satiety and drains both their glucose and fat fuel tanks. We’ll discuss this more in Scenario 5, but first, let’s touch on the low-fat, high-carb scenario.
Scenario 3: Low-Fat, High-Carb Diet
In the high-carb, low-fat scenario, someone will deplete their blood fats despite continually filling their blood glucose and glycogen stores, as long as they are not eating a significant amount of fat. Hence, stored body fat will flow back into their bloodstream to be used for fuel.
While a low-fat diet can definitely lead to weight loss, the reality is that very few people can sustain a diet with low enough fat to drive fat loss over the long term unless they adhere to an ultra-strict whole food plant-based diet.
As the chart below from our satiety analysis shows, very few people manage to maintain a very high-carb, low-fat diet. Instead, they gravitate back towards foods that mix carbs and fat, which allow them to consume more calories as they fill all of their fuel tanks simultaneously.
When it comes to fuelling weight loss, low-fat and low-carb diets restrict different macronutrients, but their effects are similar. When consuming fat-and-carb combo foods that fill up your fat and glucose fuel tanks simultaneously, the body can quickly become overwhelmed with too much energy. Thus, we only fill one fuel tank when we minimise or eliminate one of these energy sources.
It’s interesting to note that, as shown in the chart below from our satiety analysis, we tend to achieve a similar reduction in overall calorie intake by reducing either carbs or fat.
The following heat map chart from our satiety analysis of data from Optimisers shows the relationships between non-fibre carbs, fat and calories. The blue areas in the bottom left corner represent the lowest calorie intakes, while the red areas represent the highest.
From this, we can see clearly that people who are able to eat the least tend to get a higher percentage of their energy from protein and less energy from fat and/or carbs.
This brings us to our final scenario.
Scenario 4: Adequate Protein, Lower Carb & Lower Fat
In our final scenario, we have a nutrient-dense diet lower in both fat and carbohydrates that provides adequate protein.
When we eat, sufficient protein and nutrients are what we truly require. Carbs and fat are simply fuel sources that we don’t need as much of if we have plenty of energy in our systems as unwanted body fat or glucose in our liver and blood.
Once we dial back both dietary fat and dietary carbs, we can deplete the carb and fat fuel tanks in our body so our body fat can flow back into our bloodstream to be used.
Foods with a greater nutrient density and a higher protein percentage, or percentage of total calories from protein, tend to be hard to overeat. Nutrients from low-energy, nutrient-dense carbs that are fibrous also tend to fill us up. With time, body fat can flow back into the bloodstream from storage.
In the carb vs fat heat map below, the red areas align with the highest nutrient density. Notice how they also tend to align with the lowest calorie intake? When you give your body the nutrients it requires and dial back the energy from carbs and fat, your body is much happier to get on with using the excess glucose and fat stored on your body.
How Do You Know What Your Ideal Diet Is?
While you don’t have to jump into a super high protein extreme, gradually ratcheting back easily-accessible energy from carbs and fat while getting adequate protein and nutrients is THE secret to fat loss.
For more on why we don’t recommend you jump quickly to a super high protein % diet, see Secrets of the Nutrient-Dense Protein Sparing Modified Fast.
In our four-week Macros Masterclass, we walk Optimisers through dialling up their protein and fibre while scaling back their fat and carbs to find the balance that makes them feel their best.
The chart below is taken from our satiety analysis of our Optimiser data. As you can see, the average protein intake of around 15% of calories tends to align with the lowest satiety outcome and most significant energy intake.
If we can progressively reduce energy from carbs and fat and increase the percentage of our total calories from protein, we will optimise our satiation, consume fewer calories, and drain our carb and fat fuel tanks.
- To use your blood glucose to guide when you eat, to ensure you are progressively depleting the glucose in your blood to allow your body to use your stored body fat, you can check out our Data-Driven Fasting Challenge.
- To understand your current diet and how you can progressively dial back energy from fat and/or carbs, you can check our Macros Masterclass.
- To jump straight into nutrient density to give your body everything it requires without excess energy, you can check out our Micros Masterclass.
Data-Driven Fasting Index
- Data-Driven Fasting
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- FAQ #1 – What makes DDF different?
- FAQ #2 – Getting ready
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- FAQ #4 – WHEN to eat
- FAQ #5 – WHAT to eat
- FAQ #6 – Winning the mind game
- FAQ #7 – Understanding your unique metabolism
- FAQ #8 – Troubleshooting
- FAQ #9 – Things that affect your blood sugars (other than food)
- FAQ #10 – Moving on…
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