Your body has the ability to burn both fat and carbohydrates for energy, but given the choice, your body will choose carbohydrates because it's the quickest and easiest route, and the one that requires the least immediate energy. But burning fat vs. glycogen (the storage form of glucose from carbohydrates) can be more advantageous; you just have to train your body to get there.
In addition to weight loss, other benefits of burning fat for energy (a metabolic condition called ketosis) include improved mental focus, reduction in sugar cravings, better skin, improved cholesterol levels and balanced blood glucose levels. The easiest way to switch your body from burning glycogen to burning fat is by restricting your intake of dietary carbohydrates.
Burning fat vs. glycogen can promote weight loss, increase your energy levels, balance your blood sugar and improve your concentration. To turn your body into a fat-burning machine, you have to deplete the glycogen stored in the liver and the muscle glycogen stores by following a low-carbohydrate diet.
Using Glycogen for Energy
When you move, especially during exercise, your body requires a fuel source, or energy, to operate. The two major energy sources are carbohydrates and fat, but if given the choice, your body will choose carbs. When you eat carbohydrates, your body breaks them down into a simple sugar called glucose. The presence of glucose in the blood signals the pancreas to release the hormone insulin, which does one of two things with the glucose.
First, insulin carries glucose to your body's cells where it will use whatever it needs for immediate energy. After your body uses all the energy it needs in that moment, the rest is converted to a compound called glycogen. In simple terms, glycogen is a bunch of glucose molecules stuck together and saved for later. Insulin then carries glycogen to the liver and muscles where it's stored for later.
When you're not getting energy directly from food, your body turns to glycogen. Through a process called glycogenolysis, another compound called glucagon travels to the liver, where it converts glycogen back into glucose and releases it into the bloodstream. This provides fuel for your cells until the next time you eat.
The Glycogen Burning Cycle
What is the connection between glycogen and fat burning? Here's the caveat: Your liver and muscle glycogen stores can only hold so much. The total amount of glycogen that you can store in your entire body is approximately 600 grams. Once these stores max out, any excess glycogen is converted into a type of fat called triglycerides. Triglycerides can either enter directly into the bloodstream for energy, or they're stored in your body fat.
If you continuously eat carbohydrates in any form, your body will prioritize them, and the cycle will continue. This means that you'll always be burning glucose and glycogen for energy, and any excess will always get stored as body fat. When you're taking in more carbohydrates than the body can effectively store as glycogen (more calories in than out), it has no choice but to convert some and store it inside the fat cells.
If you consistently overeat, or you eat a lot of sugar and carbohydrates, this can actually cause weight gain over time.
Using Fat for Energy
In order to switch from glycogen to fat burning, you have to prevent your body from getting access to glucose and glycogen. How do you do that? By restricting carbohydrates and eating fat instead.
When you restrict carbohydrates, your body has to turn somewhere else for energy, so it goes to the next best thing: fat. After glycogen stores are depleted, your body will start breaking down fatty acids into energy-rich substances called ketones through a metabolic process called ketosis. This is beneficial because your body gets the fatty acids from your own fat stores, which can promote weight loss.
If you rely on glycogen for energy, you'll eventually reach the point where you run out, unless you're consistently refeeding (or eating more carbohydrates to replenish your depleted glycogen stores). On the other hand, if you switch to burning fat instead, you'll never run out because your body has an unlimited ability to store fat.
Burning Fat vs. Glycogen Advantages
Another advantage of burning fat vs. glycogen is increased and sustained energy. Have you ever noticed that some people crash mid-day while others stay energized? Or how some runners make a marathon look easy, while others hit the wall or don't finish? Or how some people never seem to gain weight, while others struggle severely with weight loss? The difference lies in whether or not they're burning fat vs. glycogen.
Research conducted by the Department of Human Sciences at Ohio State University demonstrated the benefits of burning fat vs. glycogen in a study published in Metabolism in 2018. Researchers took 20 male endurance-trained athletes and split them into two groups: high carbohydrates and low carbohydrates.
After 12 weeks of endurance training, they found something striking. Not only did the low-carb group experience a significantly greater decrease in body mass, but they also demonstrated improved body composition, athletic performance and fat oxidation during exercise as well.
Other Benefits of Fat Burning
Switching to burning fat vs. glucose may also increase your metabolism and promote faster weight loss. One study, published in StatPearls in 2019, showed that restricting your carbohydrate intake can lead to significantly greater weight loss than restricting the amount of fat you eat.
According to the report above, study participants who followed a low-fat diet experienced a drop in basal metabolic rate, or the amount of calories burned at rest, of almost 400 calories per day more than those who followed a very low-carbohydrate diet.
Other benefits of fat burning, or ketosis, include:
- Reduced appetite
- Reduced inflammation
- Decreased triglycerides
- Increased HDL (or "good" cholesterol)
- Decreased LDL (or "bad" cholesterol)
- Reduced blood sugar and insulin levels
- Reduced blood pressure
- Reduced sugar cravings
How to Burn Fat
Whether you call it the "keto diet," "low-carb high-fat (LCHF)" or "fat adaptation," the same principle applies. To become efficient at burning fat vs. glycogen, you must significantly decrease your carbohydrate intake and increase your consumption of good fats. If you want to deplete all of the glycogen stored in the liver and switch to burning fat instead, you may need to overhaul your diet.
Start by reducing your total carbohydrate intake to no more than 10 percent of your diet and increasing your intake of good fats. Fat should provide around 70 to 80 percent of your calories. The rest should come from protein. If you're following a 2,000 calorie diet, this means you'll eat no more than 50 grams of carbohydrates, 155 to 178 grams of fat and 50 to 100 grams of protein.
Good Sources of Fat
If you're not used to eating this way, it can be difficult to meet your fat intake at first, but it will become easier as you get used to your new dietary plan. Some good fat choices include:
- Coconut oil
- Olive oil
- Grass-fed butter
- Grass-fed beef
- Nuts and seeds (in moderation)
Ways to Increase Fat Burning
In addition to watching what you eat, pay attention to when you eat. Intermittent fasting, or going extended periods of time without food, can increase fat burning and stimulate autophagy, a process that helps detox your body and cleanse your cells.
You can also increase glycogen burning by strategically planning your workouts. Exercising on an empty stomach can quickly deplete glycogen stores and force your body to turn to fat instead. Incorporating a lot of high-intensity, aerobic workouts will help speed up the process too.
High-intensity workouts require greater amounts of glycogen, which means your body will break it down faster to meet the body's increased demands. Once the glycogen stores are gone, your body switches to fat burning.
The Importance of Hydration
Proper hydration is vital all the time, but it's especially important when you're in a fat-burning state. When you're burning fat vs. glycogen, you naturally lose a lot of excess water and the electrolytes that are dissolved in that water. Because of this, you'll need to make sure you're replenishing both your water and your electrolytes.
You can drink plain water or water flavored with a little fresh lemon. You can also make your own electrolyte replacement drink by adding a pinch of Celtic sea salt to some water with lemon. Unlike table salt, Celtic sea salt contains trace minerals, like potassium, magnesium and calcium, that combine with the sodium to replenish electrolytes and prevent dehydration.
Read more: 12 Ways to Make Water Taste (Much) Better
Burning Fat vs. Glycogen Signs
Remember, burning fat instead of glycogen, or fat adaptation, doesn't happen overnight. Once you're dedicated to a high-fat, low-carbohydrate lifestyle, it can take three to four days to switch from burning glucose and glycogen to burning fat instead. And once you start burning fat, it can take a little time after that to start feeling all of the positive effects.
In fact, you may even feel worse before you feel better. This paradoxical phenomenon is called "keto flu" and there are some tell-tale signs that happen when you first make the switch. These signs of fat-burning include:
- Weight loss
- Muscle cramps
- Changes in sleep
- Bad breath
Typically, the "keto flu" lasts for a few days and then dissipates and gives way to some of the initial positive benefits of burning fat vs. glycogen, like weight loss, increased energy and better concentration.
- Metabolism: Keto-Adaptation Enhances Exercise Performance and Body Composition Responses to Training in Endurance Athletes
- Nutrition Reviews: Fundamentals of Glycogen Metabolism for Coaches and Athletes
- Cleveland Clinic: A Functional Approach to the Keto Diet with Mark Hyman, MD
- StatPearls: Ketogenic Diet
- Medical News Today: What Are the Signs of Ketosis?
- Dr.Axe.com: Sea Salt: Top 6 Essential Health Benefits
- National Council on Strength and Fitness: Converting Carbohydrates to Triglycerides
- Diabetes: Measurements of Gluconeogenesis and Glycogenolysis: A Methodological Review
- Diabetes Forecast: How the Body Uses Carbohydrates, Proteins, and Fats
- Harvard School of Public Health: Diet Review: Ketogenic Diet for Weight Loss
- Dr.Axe.com: Benefits of Autophagy, Plus How to Induce It
- Nutrients: Regulation of Muscle Glycogen Metabolism During Exercise: Implications for Endurance Performance and Training Adaptations
- Dr.Axe.com: Working Out On an Empty Stomach: Does It Burn the Most Fat?
- Harvard Medical School: What Is Keto Flu?