Maybe you’ve heard it before, but what specifically does it mean? What implications does it have actually on health and also weight control?

This expression has been resurrected lately through the renewal in popularity of ketogenic diets (aka, low-carbohydrate, low-carb diets) and their role in ketosis.

I’ll comment on these in context below.

If you’ve ever taken a college biochemistry course then probably you have the right to still recall several of this v a distant haze the pot smoke and also hangovers (if you’re a college student reading this now, put down that joint!).

If you’re just a health and wellness enthusiast and also curious to recognize this carbohydrate flame point a little bit better, then pay nearby attention and I’ll try to store this as logical and also understandable as possible.

You are watching: Fat burns in a carbohydrate flame

Disclaimer: physiology and also biochemistry room complex, so I have actually only provided an extremely an easy overview of metabolic pathways and cellular processes as it applies to comment the carbohydrate flame question.

“Carbohydrate flame” backstory

Before you deserve to understand the “carbohydrate flame,” it’s necessary to collection the phase by mentioning two metabolic conditions:

Normal, well fed problems (i.e., 24 hour supermarkets, quick food top top every corner).No-carb or low-carb intake, fasting, starvation problems (i.e., you’re Tom Hanks stranded ~ above a southern Pacific island – WILSON!!).

Normal, well-fed conditions

Under regular conditions, friend rely mostly on three energy-containing nutrients:


In digestion, carbohydrate is broken down right into glucose, protein to amino acids, and also fat to fat acids.

These are absorbed and taken up to be save for later on or burnt now for energy.

MacronutrientBroken down to
FatFatty acids
ProteinAmino acids

Carbohydrate is your central nervous system’s desired high-octane fuel (i.e., your brain and nerves). Obtained it? remember this since you’ll watch it again.

Your human body stores carbohydrate in the liver and muscles (called glycogen) and also it have the right to be broken down at rest (i.e., liver glycogen to preserve blood sugar) or in time of require (i.e., muscle glycogen come fuel exercise, slay the saber-toothed tiger, etc).

Fat is also used together a fuel resource at rest and during prolonged exercise, as is protein come a lesser level under particular metabolic conditions.

Energy creating metabolic pathways

There are two energy pathways by which your body liberates energy from the foods items you eat:

GlycolysisKrebs bicycle (also referred to as the tricarboxylic mountain cycle or TCA cycle)

Glycolysis is the pathway you usage to break down carbohydrate.

The Krebs bicycle is the pathway you usage to fully oxidise (burn) glucose and also fatty acids down to carbon dioxide and water (and amino acids, yet not together a key fuel source).

For the purists the end there, yes, i knowoxidative phosphorylationin theelectron transfer chainalso generates a most ATP, but I’m focusing on the Krebs cycle for simplicity’s sake.

These cycles both liberate the chemical power stored in food and produce adenosine tree phosphate (ATP), i beg your pardon is favor your body’s chemistry “money” it needs to “pay” for different chemical and also physiological “transactions” (i.e., muscle contraction, cellular reactions, etc).


Glycolysis translates to “glyco” which way glucose (or sugar) and “lysis” which means splitting or breaking down, therefore it’s a sugar-splitting or sugar-breaking down process. Note: you perform not burn fat in the glycolytic pathway.

One molecule of glucose consists of six carbons. It goes v glycolysis and also is damaged down right into two 3-carbon molecule of pyruvate.


To fully oxidise glucose, pyruvate is transferred inside the mitochondria whereby it is further damaged down come a 2-carbon molecule called acetyl coenzyme A (acetyl coA) – the various other carbon is flicked turn off in carbon dioxide.

Photo credit: Wikipedia Commons. For educational usage only.

Acetyl coA then enters the Krebs cycle, combining v oxaloacetate to form citrate, and eventually passing with the whole cycle, down with the electron transfer chain wherein it have the right to be broken down right into carbon dioxide and water.

Credit: Because that educational purposes only.

Recall from above, the entire process generates power in the form of ATP i beg your pardon is prefer a “chemical currency” to “pay” for different metabolic “transactions” such as muscle contraction.

Krebs cycle for fat oxidation

What about burning fat? exactly how does the work?

Enter the Krebs cycle.

Your body stores fat together triglycerides and can rest them under for power (such as when you walk for a long run or bicycle ride).

The surname “triglyceride” describes fat’s chemical structure. A triglyceride has three (tri) fatty acids connected to a glycerol (glyceride) molecule.


When it’s time to burn fat, your body breaks under the triglyceride into cost-free glycerol and fatty acids.

The fatty acids circulate in the blood come the target tissue, speak muscle because that example.

The fatty mountain enters the muscle cell and is transported to the within of the mitochondria.

There, 2-carbon fragments at a time room cleaved turn off the fatty mountain to develop one molecule that acetyl coA.

This process is known as beta-oxidation.

This acetyl coA feeds into the Krebs cycle and is processed the an extremely same means as glucose as described above.

Quick recap

Under typical circumstances, when you’re eating plenty of carbohydrate and also fat, your body produces lots of acetyl coA indigenous pyruvate (from glucose) or from fat acids via beta-oxidation.

Both glycolysis and the Krebs cycle mite over unimpeded and there is tranquility on Earth.

However, things can go a bit haywire under fasting or starvation conditions.

I’ll describe the “carbohydrate flame” in paper definition in the next section.

Fasting or starvation conditions

Let’s speak you decide to go on the high protein, high fat pig’s feet and mayonnaise diet and your day-to-day calorie input is hovering about a meager 500 calories.

What happens to your glycolytic and Krebs cycle power pathways?

First, your body offers up its save on computer carbohydrate (glycogen) in her liver and also muscles.

Glycogen stop a little of water also so, together you diminish your glycogen, water will certainly go through it.

You’ll experience a little of fast weight lose on the bathroom scale.

You’re out of glycogen, so now it’s time to begin robbing Peter to salary Paul – metabolically speaking.

Second, together you’ll recall, your central nervous mechanism prefers glucose as its major fuel source.

If carbohydrate is not easily available, then her body deserve to make new glucose native non-glucose resources in a procedure known asgluconeogenesis(gluco = glucose, neo = new, genesis = formation).

Glucose deserve to be make from amino acids, glycerol (from triglycerides), lactate, and even oxaloacetate. (Further analysis on gluconeogenesis here).

Under common metabolism with ample glucose availability, oxaloacetate is readily available to combine with acetyl coA to form citrate which then stokes the Krebs cycle.

Oxaloacetate is generally replenished from within the Krebs cycle but can likewise be do from pyruvate.

But because you began the new low- or no-carb diet, you have depleted all your glycogen stores, slowed under the (glucose-fueled) Krebs cycle, and also depleted your capacity to make oxaloacetate from pyruvate and pyruvate native oxaloacetate.

In this certain scenario, you’re kind of boxing yourself in indigenous both ends and also creating a “metabolic traffic jam.”

Your body deserve to send acetyl coA come the Krebs bike (from fatty acids), but it requirements to have oxaloacetate obtainable to integrate with Acetyl coA.

It is through this understanding that “fat burns in a carbohydrate flame.”

More specifically, it could be stated that fat burns in an oxaloacetate flame but, since you’re unable to replenish her oxaloacetate indigenous glucose,then your interior metabolic conditions favour the formation of ketones (or ketone bodies) for power (ATP) production.

Ketosis and ketone formation

Glucose is your main nervous system’s preferred fuel source, yet when you’re in famine mode, gluconeogenesis is unable to develop adequate glucose from dietary carbohydrate so her body calls for an alternate fuel source.

In an answer to either starvation (WILSON!) or a very low carbohydrate diet,hormone alters induce thebreakdown of triglythrade from fat tissue and also favour the development of ketones (or ketone bodies) in your liver.

The ketone bodies space then released by her liver right into the blood and also are take away up and also oxidised by heart, muscle, and mind tissue which contain one enzyme to convert ketones (primarily beta-hydroxybutyrate) earlier to acetyl coA.

Acetyl coA then feeds right into the Krebs cycle to create ATP (the “chemical currency” referred to earlier).

When you lastly get rescued from the island and have a meal again (or walk off of her low-carb ketogenic diet), her body will down control ketone production and revert back to making use of carbohydrate as a fuel source again.

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Ketogenic diets are fairly trendy and also popular these days and there is evidence that they provide sustained health and wellness benefits in part people.

And, ~ above the various other hand, there space reports that lower carbohydrate dietary trends favouring animal-derived protein and also fat sources were connected with higher mortality, contrasted to plant-derived protein and fat sources (vegetables, nuts, grains) which were associated with reduced mortality.