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Burning Fats vs Carbohydrates (4 Things You Must Know)

Michael Garrico
Published by Michael Garrico
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: August 25, 2022

Our body has two sources of fuel - carbohydrates and fats. Although carbohydrates are the body’s primary energy source, from a fitness perspective, the desirable fuel you want to burn is fat.

During my fitness career, I met clients whose burning mechanisms were in stark contrast since their body composition was quite different, even though their workout plans were practically the same.

Therefore, I conducted thorough research in consultation with my dietitian to find out when and what makes the body resort to fat or carbohydrates as a fuel.

Here’s what I found out.

Quick Summary

  • Carbs and fats are both body's energy sources that it stores in the form of glycogen or fat cells.
  • A person whose diet consists of high-carb meals can have unstable blood sugar, preventing fat loss and leading to frequent energy crashes (followed by irritation and tiredness).
  • Energy for exercise comes from both sources, but in the first 30 minutes of the session, the body is burning carbs, and after that, it starts switching to fat as fuel.

Fat Burning vs. Carbohydrate Burning - What’s the Difference?

A woman using a fly machine

The main difference between fat burning and carbohydrate burning is in metabolic pathways of digesting, breaking down, and extracting energy from these two sources.

See, the carbs you eat are either transformed into blood glucose or stored as a backup in the form of glycogen - a large branched and chained molecule made of hundreds of glucose units [1].

Glycogen is stored in muscles and the liver, but when stores reach the maximum capacity, glucose gets transformed into fat in a process called 'de novo lipogenesis' [2].

Meanwhile, fat as a fuel comes from healthy fat sources in foods that get broken down into fatty acids - the building blocks of the fat molecules, with an excess stored as energy backup in fat cells.

Naturally, the body has a greater capacity for storing fat than carbs since fat is more calorie-dense and, therefore, more practical. That's why excess carbs are also stored as fat.

Generally, the body burns fat as a primary source of fuel. However, when glucose is elevated, the body secretes insulin to deal with that sugar, shutting down other energy sources and putting burning fat on pause in the process.

So, depending on your diet (but exercise and metabolism as well), your body is probably more adapted to use one of these sources more efficiently.

"Carbohydrates are broken down into glucose, which may be used as an energy source by our cells, tissues, and organs."

- Aastha Kalra, DO, Founder of Weight Zero MD 

Are You a Sugar Burner or Fat Burner?

A person doing a bench press indoors

Whether you are a sugar burner or a fat burner is determined by your workout frequency and intensity, as well as your nutrition and genetic predispositions.

There are some signs that can give away your body's preferred fuel with some certainty.

Sugar Burners

If your diet consists of pasta, cereals, and grains, your blood sugar rises high with every meal, causing the hormone insulin to rise as well to escort that sugar (glucose) into the liver, muscle, and fat cells [3].

But a few hours after a meal, insulin usually drops too much, making you feel hungry, tired, cranky, and irritable.

As a result, you struggle to lose weight and especially fat stored in the midsection.

Fat Burners

The more calories you get from nuts, seeds, meat, vegetables, and fruits, the more your blood glucose stays in check, keeping your energy levels stable and allowing your body to use predominantly fat as a fuel.

You usually feel satiated for longer and not as prone to cravings and snacking, making it easier to maintain a healthy weight. 

Besides diet, being a sugar burner or a fat burner may also be determined by your exercise choice and intensity.

Read More: Sugar Burner vs Fat Burner (Which One Are You Burning?)

Where Does Energy for Exercises Come From?

Doing cardio on a bike exercise machine

Energy for exercises comes from both carbohydrates and fats, but how many calories come from what source depends on the stored body fat, stored glycogen, and type of workout.

During the workout, your body burns both fat and carbs but at different times.

Since glucose is a fast energy source, the body will recruit the carb stores - glycogen in your liver and muscles as fuel in a process called glycolysis [4].

This fuel is depleted quickly, as glucose has only four calories of energy per gram, so it's activated in the first 30 minutes of exercises or when performing high-intensity exercise movements (anaerobic) like lifting a heavy object or sprinting [5].

After about 30 minutes, glycogen reserves start to deplete, and your body gradually switches to fat as a fuel source.

Even though fat has more calories per gram (nine), this happens later on because the process of converting fat into readily available energy is much slower.

Therefore fat metabolism is often activated during longer-lasting (aerobic exercises) like cycling, walking, and running to burn stomach fat [6].

Fat-Burning Zone

A person smiling while doing a workout

The 'fat-burning zone' principle is developed based on the switching between fat vs. carb stores.

To work out in the fat-burning zone means keeping your heart rate relatively low while performing a continuous lower-intensity cardio exercise.

It is presumed that a large number of calories you burn will come from fat.

However, overall calorie expenditure will still be higher with high-intensity workouts, meaning, you will burn more calories and lose more weight performing higher intensity exercises than lower intensity ones.

Moreover, there are studies suggesting that HIIT workouts for fat loss provide better results in terms of individual calorie burn and fat store depletion compared to continuous, moderate-intensity cardio [7].

Yet another study showed increased fat metabolism and decreased carbohydrate metabolism after six weeks of continuous training [8].

FAQs

Do You Need Carbs to Burn Fat?

Yes, you need carbs to burn fat, as burning carbs enables fat metabolism.

You need glucose to transform fat molecules into energy; otherwise, your body will use your muscle tissue to make it in a gluconeogenesis process.

Therefore, you can think of carbs as a flame that burns stored fat, which is why endurance athletes always consume some carbs before their performance.

How Do You Trick Your Body Into Burning Stored Fat?

You can trick your body into burning fat with hacks like drinking ice water, chewing gum after meals, chewing food slowly, and cooling yourself down.

However, the foundation of burning more fat should consist of proper calorie intake, healthy nutrition, and physical activity, as the aforementioned hacks can help you burn just a small amount of calories.

Will You Become a Fat Burner?

To deplete more fat stores and trigger weight loss, you must switch to an active lifestyle, eat minimally processed foods and base your diet on a calorie deficit combined with lean protein sources.

But, since it’s challenging to be consistent with these, especially with our busy schedules, I always advise my clients to support their efforts with high-quality fat burners that we tested for safety and efficacy ourselves:

These supplements are designed to fast-track weight loss mainly through thermogenesis and appetite suppression, taking into account the gender differences in metabolism.


References:

  1. https://www.sciencedirect.com/science/article/pii/S2214647416300010
  2. https://academic.oup.com/ajcn/article-abstract/48/2/240/4694971
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6331362/
  4. https://www.ncbi.nlm.nih.gov/books/NBK482303/
  5. https://www.sciencedaily.com/releases/2007/06/070618124541.htm
  6. https://www.gssiweb.org/en/sports-science-exchange/Article/regulation-of-fat-metabolism-during-exercise
  7. https://pubmed.ncbi.nlm.nih.gov/22648463/ 
  8. https://pubmed.ncbi.nlm.nih.gov/19088769/

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