Everything You’ve Ever Wanted to Know About Fat Burning

Written and medically reviewed by Rich LaFountain, PhD

Your body wants to burn fat.

When you’re regularly burning fat for energy, your body reacts in all sorts of ways that help you avoid metabolic disease, like maintaining a healthy weight, controlling glucose, and reducing inflammation. However, if you’re like most people, you’re stuck in a never-ending sugar-burning cycle, which — if it hasn’t already — can turn into insulin resistance, obesity, and chronic age-related disease.

The good news is you can tap back into your body’s inherent fat-burning ability with relative ease. Zero is one of the simplest, most reliable ways to accelerate fat burning so you can lose weight… without also losing your sanity.

What’s Fat Burning, Anyway?

Fat burning describes the processes that your body uses to turn either fat you recently ate or fat stored in your body into energy. These processes activate when glucose and insulin levels approach a natural baseline, indicating to your body that you need another source of fuel. And when does that happen? When you haven’t consumed glucose for a while — specifically after an overnight fast lasting at least 12 hours.

For hundreds of thousands of years, humans regularly feasted when food was plentiful and fasted when food was scarce. This is why you have a massive inborn fat-burning capacity: Your ancestors needed it to survive. It’s only in the last hundred years or so that modern conveniences have enabled round-the-clock eating every day of the week. Unfortunately, fat burning, healthy body weight, and metabolic function have become unintended casualties of this modern lifestyle.

In order to reactivate and reconnect with your natural fat-burning potential, you simply need to be intentional with your habits, especially intermittent fasting. 

Fat Burning, Weight Loss, and Fasting: They’re All Connected

To lose weight, specifically fat, you need to burn it as fuel.

There are a handful of ways to increase fat burning with lifestyle changes, namely through fasting, movement, and dietary habits. Because fasting is more tightly linked to fat burning and weight loss than physical activity or diet individually, this is the cornerstone of Zero upon which all your other complementary habits are built. Here’s how it works.

When you’ve recently eaten, your body grabs glucose for fuel, because it’s the most prevalent and easiest-to-burn substance on hand. Due to the aforementioned “modern” eating patterns, most people have more than enough glucose available from the meals, snacks, and beverages they consume to keep the proverbial “glucose fire” roaring most of the time.

Your fast begins when you take your last bite of your last meal of the day. About 4 hours later, your body is finished burning or storing glucose from the food you ate and reaches for the next-easiest fuel source: glycogen, which is glucose stored in your liver and skeletal muscles. In order to shift into fat burning, you must burn through a significant proportion of your stored liver glycogen. If you start eating again before you’ve done that, you’re essentially staying on the “glucose treadmill” without ever tapping into your fat-burning reserves. (And you have a lot of reserves. Your body has 60 times more energy stored as fat than as glycogen!)

After about 12 hours, your low glycogen stores signal to your body that you need a new primary fuel source — and this is when your body starts really reaching for fat. The reason fat is a “slower-burning energy” is because unlike glucose and glycogen, which readily burn within your cells, fat burning occurs one layer deeper, inside structures within your cells called mitochondria. This means that your body needs to break down stored fats into lipids (i.e., smaller units) and transport those lipids not just into the cells but into the cells’ mitochondria for combustion. All of the cellular machinery involved in this process gets better with use — and worse with disuse — so, if you want to be a great fat burner, you need to regularly signal the importance of fat burning to your body so it keeps this pipeline in pristine condition.

Become a Better Fat Burner

You were born with an impressive fat-burning ability, but if you’re like most people, you’re probably under-utilizing it, thereby diminishing your fat-burning ability over time. To reactivate your fat-burning potential, fasting long enough to burn through your body’s other fuel reserves is the first step; extending your overnight fast to 12–18 hours increases your reliance on fat for energy by roughly 25%

This will get your fat-burning fire lit, but if you want to get the fire white-hot and maximize your fat-burning potential, there are several other things to do during your fast.


One of the best tools you have for promoting mitochondrial health and enhancing fat burning is exercise, specifically fasted exercise. A brisk walk or other light-to-moderate exercise before breaking your fast increases your fat-burn rate by roughly 1 gram of fat per 10 minutes you are active.

Furthermore, research suggests that your fat-burn rate is nearly 100% higher during subsequent movement if you “prime the system” with a previous bout of activity. In other words, fasted exercise not only burns more fat than “fed” exercise, but it also sets you up to maximize fat burn for the rest of the day as you engage in your regular daily activities.


Optimal fat burning relies on sufficient sleep. To get the most out of your fast, you’ll want to stop eating 2–4 hours before bed and then sleep for 7–9 hours. Quality matters, too; the higher quality your sleep, the better you’re supporting healthy metabolic function and, in turn, your fat-burning ability.

Reduce Stress

Chronic psychological stress can slow your fat burning. Therefore, engaging in leisurely, enjoyable activities during your fast can help prevent chronic stress from putting the brakes on your weight-loss journey. Something as simple as being mindful while you enjoy your morning cup of coffee can be enough. (Plus, coffee is a thermogenic and a lipolytic, so it will increase your total energy burn rate in addition to freeing more fat from storage so it can be burned more easily!)

Conclusion: Activating Fat Burning with Fasting Helps You Burn Fat and Lose Weight

Human nutrition and lifestyle have changed a lot over the last two centuries. Unfortunately some of these shifts toward convenience have likely inhibited your natural fat-burning potential. If you want to activate fat burning and experience simultaneous weight loss and metabolic health benefits, get intentional about intermittent fasting (and complementary fat-burning habits!) with Zero.

Bonus: The Fat-Burning Glossary

While we try to make weight loss as simple as possible, the science can be complex, and the biggest barrier is often the terminology. Save this glossary for the next time you’re scratching your head or trying to follow along with your own fasting physiology!

  • Glucose: The most important fundamental carbohydrate in the body, glucose is a six-carbon molecule that provides energy.
  • Insulin: A hormone that moves glucose from the bloodstream into cells, where it can be burned for energy; a strong inhibitor of lipolysis (fat breakdown).
  • Lipid: A compound that is insoluble in water, lipids are contained in dietary fat and oils as well as wax and steroid hormones. Lipids are found in the membrane of each of your body’s trillions of cells.
  • Lipolysis: The breakdown of lipids — stored as triglycerides in fat cells — to fatty acids that the body can burn for energy.
  • Fatty acid: A hydrocarbon chain that varies in length, is energetically dense, and provides 9 calories of energy per gram.
  • Beta-oxidation (also β-oxidation): The process by which fatty acid chains are broken down into small two-carbon molecules for energy production.
  • Metabolism: All of the chemical reactions that occur throughout the body and within cells, often used to reference the breakdown of molecules that provide energy.
  • Metabolic switching: The body’s process of transitioning between fuel sources, particularly from primarily glucose to primarily fatty acids and ketones.
  • Ketone bodies: Small molecules produced during fat burning that can be used as an energy source for organs, like the brain and heart, and have hormone-like functions.
Rich LaFountain, PhD
Posted in Health & Science

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