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Carbs, Fats Or Proteins | What's The Best Fuel For Your Body

By Tyler Woodward

Carbs, Fats Or Proteins | What's The Best Fuel For Your Body

In your lifetime you’ve likely heard it all. Eat more protein to lose weight, carbs are killing you, fat makes you fat, but do any of these assertions actually hold up? This leaves the question, protein, carbs or fats or is one truly better than the others?

A Tale Of Four Metabolisms...

Key Takeaways:

Today, it’s been established that there is one quintessential law that dictates whether you gain, maintain or lose weight, known as energy balance.

Energy Balance:

Energy Balance

Energy balance is the concept of calories in vs. calories out. Calories are a measurement of energy, more specifically a measure of the amount of heat produced. 

  • Calories in > Calories Out - If you eat more calories than you burn you will gain weight as either fat or muscle if you are resistance training.
  • Calories in < Calories Out - If you consume fewer calories than you burn you will “burn fat” and lose weight.
  • Calories in = Calories Out - If you burn as many calories as you consume you will maintain your weight

The amount of calories or energy you burn is determined by your metabolic rate or metabolism. Metabolism is defined as, “the sum of the [energy of the] chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material”.

Read More: The Weight Loss Equation

The question then becomes which macronutrient; protein, carbs, or fat produces the most energy?

Proteins, Carbs or Fat?:


You may have heard that you should eat tons of protein to burn fat because your body must convert it to sugar (carbohydrates) or fat in order to be used as energy, which “burns more calories”. While this sounds like an easy way of tricking your body to burn more calories, it doesn’t actually work like this. 

As you know protein, more specifically amino acids cannot be used directly as energy. In order to convert amino acids into usable energy the amino acids must be converted into pyruvate (pyruvic acid) and ammonia. Ammonia is a toxin that must be excreted in the body as urea. While your body is readily capable of detoxifying this ammonia, it is an extra stress that requires an additional input of energy to be broken down. This results in protein being a very inefficient source of energy and serves as a backup energy reserve to carbs and fats. 

Carbs vs. Fats?:


Well it turns out that gram for gram carbs and fats yield nearly the same amount of total energy.  Both fats and carbs must be converted into acetyl CoA  to be used for energy at which point the energy production process is identical, but the difference between them lies in how they get there.

  • To get 1 molecule of Acetyl CoA from glucose you get 1 CO2 molecule and 2 molecules NADH.
  • To get 1 molecule of Acetyl CoA from fat you get 1 NADH molecule and 1 FADH2

In the mitochondria (the engine of the cell) you need more NADH relative to FADH2, but for the purpose of this article we’ll just refer to this as an added bonus for glucose metabolism. The real kicker in glucose metabolism is the extra CO2 produced. 

Learn More: The Benefits Of Sugar

CO2, Just A Waste product?:


Carbon Dioxide or CO2 is arguably the most underrated compound in the human body. Commonly referred to as a “waste product” of metabolism, I can promise you that it is anything but. While carbon dioxide has a ton of beneficial effects on the body, in regards to metabolism and cellular respiration it is just as essential as oxygen. 

Since your first elementary school class you were likely told that you breathe in oxygen and you breathe out carbon dioxide. This holds true even to the cellular level, except in order for your cells to take in/absorb oxygen they must release carbon dioxide. 

Hemoglobin is the main protein present in your red blood cells and is responsible for binding to oxygen in the lungs and delivering it to the cells in your tissue. Hemoglobin is also responsible for transporting the carbon dioxide produced from your cells into the lungs and out of your body. In order to transport both oxygen and carbon dioxide, hemoglobin must physically change shapes. In more acidic environments like your tissues, hemoglobin conforms to its “T” shape where it absorbs carbon dioxide and releases oxygen. In a more basic environment like your lungs, hemoglobin changes to it’s “R” shape where it releases carbon dioxide and absorbs oxygen. These are known as the haldane and bohr effects respectively. 

Why Is This Important?

Because the more carbon dioxide that your cells produce, the more oxygen they are able to absorb. The more oxygen they can absorb the more they can use to create energy. Since sugar/glucose metabolism releases more carbon dioxide than fats it results in a feedback loop of more energy production in your cells. 

↑CO2 released ->↑ O2 absorbed -> ↑Energy Produced

Glucose metabolism is so efficient because it uses oxygen at the same rate as it releases carbon dioxide in a 1:1 ratio. The ratio of oxygen used/ carbon dioxide produced is known as the respiratory quotient. The respiratory quotient of each macronutrient is as follows:

  • Carbohydrates =1
  • Fatty Acids ~ .7
  • Proteins ~ .8-.9 

Another way to think about this is that for fatty acids every 10 O2 molecules that are used results in 7 CO2 molecules or for proteins 10 O2 for 8-9 CO2.

As long as you have enough glucose in supply through eating sugar and your liver’s glycogen stores (glucose storage) you will continually upregulate the energy consumption of your cells. 

↑Energy Consumption = ↑ Metabolic Rate

So sugar due to its 1:1 ratio of O2 consumption to CO2 release literally has the ability to increase your energy expenditure or metabolic rate. 

It might be easier to think of this in terms of cars and their engines

  • Sugar metabolism is like a self-sustaining car that runs off its own energy and releases no useless fumes into the environment.
  • Protein & fat metabolism in this analogy use more energy and release more emissions polluting the environment. 

The key to sugar's ability to increase your metabolism is the presence of oxygen and the use of oxidative phosphorylation or cellular respiration. If your cells cannot absorb oxygen then they are forced to rely on anaerobic respiration or anaerobic glycolysis. This is the production of energy using sugar without oxygen. 

Read More: The Sugar Secret

Anaerobic Respiration:

anaerobic exercise

Glycolysis (the first step in cellular respiration/ sugar metabolism) does not require oxygen, so the end products are the same: 2 molecules of pyruvate, 2 molecules of NADH, 2 ATP & 2 CO2. 

Normally, when oxygen is present these pyruvate molecules are converted into Acetyl CoA where they are taken through the electron transport chain and produce a ton of energy as ATP. The electron transport chain requires oxygen, so when oxygen is not present these pyruvate molecules cannot be used to create more energy. In order to produce more energy these 2 pyruvate molecules are converted into 2 molecules of lactic acid and 2 molecules of NAD+ as a result. The production of NAD+ through the formation of lactic allows for glycolysis and thereby energy production to continue without oxygen.

Lactic acid or lactate is also a toxin in the blood and must be converted in the liver back into glucose which takes 6 ATP. In total, anaerobic respiration actually results in a net loss of 4 ATP and negative energy production since glycolysis results in 2 ATP per 2 lactic acid molecules and requires 6 ATP to be converted back into glucose.

Anaerobic respiration is said to have a respiratory quotient of ∞ because it doesn’t use any oxygen and produces carbon dioxide. This is extremely toxic to the body because it results in an energy debt. 

Read More: The Importance Of Micronutrients: The Secret To Staying Healthy For A Lifetime

Energy Production Revisited:

Aerobic Respiration

Knowing this information we can now rank each energy source or metabolism in order of efficiency:

  1. Cellular (Aerobic) Respiration - Glucose + Oxygen
  2. Fatty Acid Metabolism (Beta Oxidation) - Fat + Oxygen
  3. Protein Metabolism (Gluconeogenesis) - Protein conversion into sugar
  4. Anaerobic Respiration (Glycolysis) - Glucose without oxygen

It’s also worth noting that the only form of stored energy in the body that does not require the breakdown of your body’s own tissue is glucose. 

  • Glucose requires the conversion of glycogen back into glucose (glycogen is not a living, breathing part of your body a tissue, its solely stored energy)
  • Fat requires the breakdown (lipolysis) of fat cells into fatty acids
  • Protein requires the breakdown of skeletal muscle into amino acids

This is not to say that using protein or fat as fuel is “bad”, but they are less efficient fuel sources in the body. Both require the release of stress hormones like adrenaline and cortisol and the breakdown of bodily tissue (either fat or protein sources) to be used. Certain organs in the body like the heart and muscles also prefer to use fat as fuel, so you will never be able to solely burn carbs as fuel. 

Fat is a much more efficient means of storing energy than carbs or protein, which is why it has the highest energy per gram:

  • Fats - 9 Kcal/ gram
  • Proteins - 4 Kcal/ gram
  • Carbs - 4 Kcal/gram

In order to store energy as glucose it must be converted to glycogen, but every gram of glycogen stored requires 2-4 grams of water stored as well. This is why people on the keto diet experience rapid weight loss because they are depleting their body of its glycogen stores and all the water weight comes with it. And proteins are quite literally never stored as energy, they’re either converted into sugars for energy or used to build thousands of biological compounds like enzymes, hormones, transporter molecules, muscle, the list goes on. 

Lastly, carbohydrates have the added benefit of being protein sparing, meaning that they deter the breakdown of protein to be used as fuel. 

Read More: 5 Best Supplements To Reduce Cortisol Naturally

But What If I Want To Lose Fat?:

lose fat

Remember, fat loss is driven by a calorie or energy deficit, burning more calories than you consume. Because sugar encourages an increased metabolic rate it will be the most bang for your buck fuel source for your body because it will maximize the amount of energy you  use. You want to keep the amount of fat that your body uses as energy to the minimum. This will ensure that the fat your body is using as energy you’re actually losing and is not being replaced with fat in your diet. For example, if your maintenance calorie intake is 2500 calories and you’re eating 2,000 calories daily you want as much of those 500 calories as possible to come from burning fat. It’s for these reasons that I am not a proponent of intermittent fasting or the keto diet because they increase the amount of fat burned as fuel without any additional benefits.

At the end of the day the law of energy balance is going to prevail, as long as you’re eating fewer calories than you burn whether it's from fat, proteins or carbs you will lose weight. The pivotal difference I would argue is that a carbohydrate dominant diet increases the amount of energy that you burn.

So here’s my proposal:

  • Consume a maintenance dose of protein - about .82 grams per pound of body weight
  • Consume as little fat as you need (or want), but make sure to consume enough to get in the fat-soluble vitamins (A, E, & K). 
    • Also, there’s no such thing as “essential fatty acids” your body can make fat from sugar when necessary
  • Fill in the rest with carbs, preferably largely from nutrient rich sources like honey, fruits, juices and starches, but have at it and throw some good ol’ sugar in as well

And see for yourself what happens...

If you want to learn how to eat to maximize your metabolic rate, look no further than our Thermo Diet Program on UMZUfit. Written by UMZU's owner Christopher Walker, the Thermo Diet takes the Bioenergetic approach to nutrition aiming maximize energy production at the cellular level and achieving hormonal balance at the systemic level. This will give you and your cells the energy to thrive today and for years to come.


My goal in writing this article, as always, is to provide you with logically-based principles that you can use to form your own conclusions regarding any information you may come across within this subject. I really hope you found this article interesting and if you have anything to add to this article, comments or criticism, feel free to reach out to me on our facebook groups or on Instagram @tylerwoodward_fit. Please feel free to share this article with anyone that might be interested!

Thanks for reading!

Until next time… be good

~Tyler Woodward
B.S. Physiology and Neurobiology