Maybe you’ve heard the before, yet what precisely does the mean? What ramifications does it have actually on health and also weight control?

This expression has actually been resurrected lately with the revival in popularity of ketogenic diet (aka, low-carbohydrate, low-carb diets) and their duty in ketosis.

I’ll talk about these in paper definition below.

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

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

You are watching: Fats burn in the flame of carbohydrates

Disclaimer: physiology and biochemistry room complex, so I have actually only given an extremely simple overview of metabolic pathways and also cellular processes as it applies to answering the carb flame question.

“Carbohydrate flame” backstory

Before you deserve to understand the “carbohydrate flame,” it’s crucial to set the stage by stating two metabolic conditions:

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

Normal, well-fed conditions

Under typical conditions, girlfriend rely generally on three energy-containing nutrients:


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

These are soaked up and taken as much as be stored for later on or scorched now because that energy.

MacronutrientBroken down to
FatFatty acids
ProteinAmino acids

Carbohydrate is your central nervous system’s wanted high-octane fuel (i.e., your brain and nerves). Obtained it? mental this due to the fact that you’ll see it again.

Your body stores carbohydrate in the liver and muscles (called glycogen) and it deserve to be damaged down at remainder (i.e., liver glycogen to preserve blood sugar) or in times of need (i.e., muscle glycogen come fuel exercise, slay the saber-toothed tiger, etc).

Fat is also used together a fuel source at rest and also during prolonged exercise, as is protein to a lesser level under details metabolic conditions.

Energy developing metabolic pathways

There room two energy pathways whereby your human body liberates energy from the foods items you eat:

GlycolysisKrebs bike (also dubbed the tricarboxylic mountain cycle or TCA cycle)

Glycolysis is the pathway you usage to failure carbohydrate.

The Krebs cycle is the pathway you usage to completely oxidise (burn) glucose and fatty acids under to carbon dioxide and water (and amino acids, but not as a main fuel source).

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

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


Glycolysis converts to “glyco” which way glucose (or sugar) and “lysis” which means splitting or break down, for this reason it’s a sugar-splitting or sugar-breaking under process. Note: you do not burn fat in the glycolytic pathway.

One molecule that glucose contains six carbons. The goes v glycolysis and is broken down into two 3-carbon molecule of pyruvate.


To totally oxidise glucose, pyruvate is transferred inside the mitochondria where it is further broken down come a 2-carbon molecule dubbed acetyl coenzyme A (acetyl coA) – the other carbon is flicked off in carbon dioxide.

Photo credit: Wikipedia Commons. For educational use only.

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

Credit: Because that educational objectives only.

Recall from above, the entire process generates energy in the form of ATP i m sorry is choose a “chemical currency” to “pay” for various metabolic “transactions” such together muscle contraction.

Krebs cycle because that fat oxidation

What about burning fat? just how does the work?

Enter the Krebs cycle.

Your human body stores fat together triglycerides and also can break them under for power (such as when you go for a lengthy run or bike ride).

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


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

The fat acids circulate in the blood come the target tissue, say 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 are cleaved off the fatty mountain to produce one molecule that acetyl coA.

This procedure is well-known as beta-oxidation.

This acetyl coA feeds right into the Krebs cycle and also is handle the very same means as glucose as described above.

Quick recap

Under typical circumstances, when you’re eating plenty the carbohydrate and fat, your body produces numerous acetyl coA native pyruvate (from glucose) or from fatty acids via beta-oxidation.

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

However, things have the right to go a little bit haywire under fasting or famine conditions.

I’ll explain the “carbohydrate flame” in context in the following section.

Fasting or famine conditions

Let’s say you decide to walk on the high protein, high fat pig’s feet and also mayonnaise diet and your daily calorie intake is hovering approximately a meager 500 calories.

What wake up to her glycolytic and also Krebs cycle power pathways?

First, your body provides up its save carbohydrate (glycogen) in your liver and also muscles.

Glycogen hold a little of water also so, as you diminish your glycogen, water will certainly go with it.

You’ll endure a bit of fast weight ns on the toilet scale.

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

Second, as you’ll recall, your main nervous device prefers glucose together its primary fuel source.

If carbohydrate is not conveniently available, then your body have the right to make new glucose indigenous non-glucose resources in a procedure known asgluconeogenesis(gluco = glucose, neo = new, genesis = formation).

Glucose can be do from amino acids, glycerol (from triglycerides), lactate, and also even oxaloacetate. (Further analysis on gluconeogenesis here).

Under regular metabolism v ample glucose availability, oxaloacetate is readily easily accessible to incorporate with acetyl coA to kind citrate which climate stokes the Krebs cycle.

Oxaloacetate is typically replenished from within the Krebs cycle yet can also be make from pyruvate.

But because you started the new low- or no-carb diet, you have actually depleted all her glycogen stores, slowed down the (glucose-fueled) Krebs cycle, and depleted your capacity to do oxaloacetate native pyruvate and also pyruvate indigenous oxaloacetate.

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

Your body have the right to send acetyl coA come the Krebs bicycle (from fatty acids), but it demands to have actually oxaloacetate obtainable to integrate with Acetyl coA.

It is v this expertise that “fat burns in a carbohydrate flame.”

More special, it might be claimed that fat burns in an oxaloacetate flame but, because you’re unable to replenish your oxaloacetate indigenous glucose,then your internal metabolic problems favour the development of ketones (or ketone bodies) for power (ATP) production.

Ketosis and ketone formation

Glucose is your central nervous system’s preferred fuel source, but when you’re in starvation mode, gluconeogenesis is can not to develop adequate glucose from diet carbohydrate so her body calls for an different fuel source.

In response to either scarcity (WILSON!) or a really low carbohydrate diet,hormone transforms induce thebreakdown of triglycerides from fat tissue and also favour the development of ketones (or ketone bodies) in your liver.

The ketone bodies are then exit by your liver into the blood and also are bring away up and also oxidised by heart, muscle, and mind tissue i m sorry contain one enzyme to convert ketones (primarily beta-hydroxybutyrate) ago to acetyl coA.

Acetyl coA climate feeds into the Krebs cycle to produce ATP (the “chemical currency” described earlier).

When you finally get rescued indigenous the island and also have a meal again (or walk off of her low-carb ketogenic diet), her body will certainly down manage ketone production and revert earlier to utilizing carbohydrate together a fuel source again.

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Ketogenic diets are fairly trendy and popular this days and also there is proof that they carry out sustained health benefits in part people.

And, ~ above the other hand, there space reports that lower carbohydrate dietary patterns favouring animal-derived protein and also fat resources were connected with higher mortality, compared to plant-derived protein and also fat sources (vegetables, nuts, grains) i m sorry were connected with reduced mortality.