Fat Oxidation Vs Fat Loss

Why Burning Fat for fuel does not always mean you are “losing weight”

Long term fat loss:  

When thinking of losing weight, you shouldn’t think about losing fat. Just like when you are exercising (if the goal is weight loss) you shouldn’t think about “burning fat”. Instead I want you to think about carbon. Assuming the objective is weight loss. The goal should be to have a net loss of carbon throughout your day.

What does Carbon have to do with losing fat?

The body’s energy source that keeps us alive is ATP, once ATP stops, life stops. In order to generate more ATP our body needs to do so with macronutrients we eat such as fats and carbohydrates. The building blocks of fat and carbohydrates is the element carbon. What is a carbohydrate? A 6-carbon molecule. What's Fat (triglyceride)? 12-24 carbon chains stuck together by a glycerol that is also made from carbon!  

See Images below: The “C”s represent carbon

At the end of the day, our body needs carbon, it is less relevant for survival on how it gets it.  

Here’s a story to hopefully bring things together:  

A father asked his twin daughters to start a lemonade stand. The child that can bring home the most dollars wins.    

The first child only thought of dollars in a literal sense of dollars cash so they made a lemonade stand with a sign that read, “accepting dollar bills only”. Because after all, that’s what her father wanted, dollar bills.  

The second child made a stand that said “Accepts all forms of payment”  

At the end of the day the first daughter had significantly more “dollar bills” so she thought she won. 

 However, the second daughter who accepted all forms of payment (Venmo and PayPal) transferred her digital dollars to the bank and withdrew from an ATM. After the withdrawal they were far ahead in total profit.  

Carbon is the currency of the human body just like cash/money is the currency of the world. The dollars we spend via credit cards, bank wires, or Venmo are not worth any less than if we paid in cash for the same product.  

So even if you burn “more fat” in a workout, what was the total amount of carbons burned?  

An individual who had an intense workout probably didnt burn much fat for fuel but they depleted glycogen storages which will need to be replenished. The next couple of meals they eat, when carbohydrates are consumed they will to be used to restore depleted glycogen. The body will use some of the other food consumed or stored fat for energy. Potentially resulting in fat loss. 

Lets see how this plays out in a hypothetical situation:

Say you had a pair of identical twins at the same weight who had a gross burn of 3k calories a day and consumed 3k calories a day each.  

Twin A eats a high fat diet or 2000 calories from fat per day, 600 calories from protein, 400 calories from carbs.  

Twin B eats a diet of 1000 calories from fat per day, 600 calories from protein and 1400 calories from carbohydrates. 

For simplicity, let's say thermogenics are not playing a role    

Twin A burns 66% of their calories from fat (RQ .80)

Twin B burns only 35% of their calories from fat (RQ .90)  

Technically, twin A is burning more fat throughout the day, so why are they the same weight?

Answer: The body will “burn” what is available to it. What you eat, you burn.  

Person A is “burning” more fat for fuel, because they are consuming more fat.   

If someone eats more fat for fuel and therefore burns more fat for fuel, this does NOT mean they are losing fat or “better” at oxidizing fat. The body is simply being efficient with what it is given.

To test how the body is at oxidizing fat for fuel, aka burning fat under stress, a metabolic assessment needs to be done. The higher the intensity (watts or speed) one can utilize fat as a fuel, the greater their ability to oxidizing fat.  

Maximum Fat Oxidation vs Burning Fat at Rest

Fat Oxidation  

Maximum Fat oxidation (MFO) is a biomarker representation of metabolic health, sub maximal performance, mitochondrial efficiency, number and volume. Fat oxidation positively correlates with training volume in zone 2, type 1 fibers and inversely correlates with blood lactate levels.  

When you hear MFO or “fat oxidation” I want you to think of the word “Oxidation”. Fat is mobilized from adipose tissues around the body and brought to the working tissue to be oxidized in the mitochondria (if it can enter). The largest amount (in grams) of fat oxidized during exercise at a given intensity represents someone's MFO or maximum fat oxidation. This is not during rest, but during exercise. It's possible to “burn” fat well at rest but have poor “fax oxidation” during exercise. Like an idling car, we are unaware of its capabilities until we start driving and pushing it.  

Burning fat.  

Burning fat as a substrate means it is the fuel source being currently used. Many factors can play into a substrate being utilized; diet is the most important at rest, and intensity is the most important during exercise.  

Healthy metabolic systems are not under stress during resting conditions; therefore, the body uses whatever fuel source is available. With a high fat diet, an individual will burn more fat for fuel at rest, and slightly more fat during submaximal exercise. This does not mean the person is “losing fat”, this only means that fat is the fuel source being used at the time, the currency which our body is using to exchange for ATP.  

A high fat diet utilizes more fat oxidation during exercise because of “glycogen sparing”. Since the body isn't receiving much carbohydrate, it saves it’s stored glycogen for necessary times. However, because carbohydrate intake is low, that means total glycogen storages are low, glycolic enzyme activity is unpracticed / inefficient and therefore peak performance or repeated sprint ability would be significantly constrained.   

Conclusion:

Burning fat at rest or exercise does not mean you are losing more fat than if you were burning carbs. Total carbon or caloric expenditure will determine your weight loss.

Just because someone “burns more fat at rest” does not mean they are metabolically superior. Instead how much fat they burn during exercise will determine the health / capabilities of their fitness and mitochondrial health. To determine this you need metabolic testing.

Carbon is the currency of the body! Don’t think of eating or burning carbs vs fats, think of eating carbons and burning carbons. 10,000 carbons burned from carbs will illicit more weight loss than 5,000 carbons burned from fat.