Metabolic Flexibility – The Making of a Fat-Burning Body

Metabolic Flexibility – The Making of a Fat-Burning Body

Video | Definition | Advantages | How to Become Metabolically Flexible | Takeaway

We have access to food around the clock and many modern foods have been refined, changing the way our bodies handle them. These changes leave our metabolisms one dimensional making it hard to switch between running on both glucose and fat.

In this post, I’ll explain how to make your body more efficient at switching between whichever fuel source is available and how that renewed metabolic flexibility will make you a better fat burner.

Article At-A-Glance

  • A metabolically flexible body can efficiently switch to running on the most available fuel (i.e. dietary glucose, stored glucose (glycogen), dietary fat, stored fat (adipose), ketones)
  • Metabolic inflexibility is a consequence of modern-day refined foods that are available 24/7 and inactivity
  • You can make your body more metabolically flexible with intermittent fasting, exercise, and a low-carb diet that emphasizes whole foods. 

Metabolic Flexibility – The Making of a Fat-Burning Body [Video]

In this video, you’ll learn…

  • The definition of metabolic flexibility.
  • What causes us to be metabolically inflexible.
  • Ways to improve our flexibility!

What Does It Mean to Be Metabolically Flexible? 

The easiest way to think of metabolic flexibility is to think of a hybrid car. Hybrids can utilize both a gas-powered engine and an electric motor to run the vehicle.

A metabolically flexible body is similar in that it runs efficiently on different fuel sources. In the case of the body, those fuels are glucose and fat.

Being metabolically flexible means that your body can efficiently switch to running on the most available fuel. At any given time, that fuel could be glucose from your diet or stored glucose, which is glycogen, dietary fat or stored fat.

If glucose is low enough, your liver turns some of the available fat into ketones, providing an additional type of fuel that is particularly beneficial to your brain. 

Metabolic flexibility is like a hybrid car

Advantages of Metabolic Flexibility

Learning how to become metabolically flexible comes with some perks.

Because your body always has an option to meet its energy needs, you experience sustained energy and freedom from hunger. And, because a portion of your energy is coming from fat, you have an easier time with weight loss. 

What Causes Metabolically Inflexible? 

Back in the days before we had highly processed foods and 24/7 access to food, our bodies had no trouble with metabolic switching. However, our eating habits and food choices have changed. 

Many of the foods that are readily available to us have been highly refined and combined with unhealthy vegetable oils.

The refining breaks down the original fiber and nutrients in the food making them absorb into our systems quickly. That quick absorption coupled with the unhealthy fat leads to insulin resistance, which is a state in which the cells resist the onslaught of energy coming to them.

If you eat multiple times a day, that constant feeding adds even more energy to your system that has nowhere to go. This nutrient overload along with the development of insulin resistance is thought to contribute to the impaired fuel switching that we see with metabolic inflexibility (1) (2).

How to Become Metabolically Flexible

If your goal is to lose weight, you want to increase your metabolic flexibility. You can do that by changing when you eat, how you move, and what you eat. Let’s take a look at each one of these. 

Intermittent Fasting 

Intermittent fasting is the practice of cycling between periods of eating and not eating or fasting. There are different ways to practice intermittent fasting but the common form is time-restricted eating meaning that you reduce or restrict the number of hours a day in which you are consuming food down to 8 to 10 hours, for example.

During those fasting hours, your body is using up the circulating glucose and then breaking down glycogen. When that energy is used up, your body must look for a new fuel source. What is available? Fat.

Fasting forces your body to go through the trouble of breaking down fat for energy. The more this is practiced, the better your body becomes at switching to fat, improving your metabolic flexibility.

Intermittent Fasting


Exercise is helpful because it improves insulin sensitivity. Insulin sensitive cells are more efficient at switching between burning glucose and fat.

While there may be an argument for intense exercise like weightlifting or high-intensity interval training being the most helpful. Any increase in physical activity will help (3).


Eat Whole (Unprocessed) Foods

What you choose to eat is certainly an important factor in this equation. The most important first step is to choose whole foods over processed and refined foods. Think of foods that still resemble the original plant or animal that they came from rather than foods that come in a box.

The slower absorbing whole foods trickle energy into your system instead of overtaxing your system with energy that must get stored. An additional step you can take is lowering the overall carbohydrate intake of your diet

Choose whole foods

Low Carb Diet

Carbohydrates breakdown into glucose. If you limit the glucose coming in, your body must move to the next available fuels, which are glycogen and fat. If enough glucose is depleted, your liver makes ketones out of fatty acids raising your metabolic flexibility to a higher level.

The interesting thing to note is that you don’t need to be on a ketogenic diet for your body to make ketones. Ketones are needed by your brain when glucose is too low, so any action you take that depletes glucose could lead to ketone production.

For instance, I do not follow a keto diet, but I do eat a low-carb diet and practice intermittent fasting, so it is not unusual for me to test my blood in the morning and notice the presence of ketones.


You can make your body more metabolically flexible and therefore train it to be a better fat burner. To do so, practice intermittent fasting, get more physically active, and reduce the overall carbohydrate content of your diet, especially refined carbs.

If you are interested in learning which foods are healthy low-carb choices, I have a downloadable list of 100 plant and animal-based low-carb foods.

low carb food list


(1) Galgani, Jose E., Cedric Moro, and Eric Ravussin. “Metabolic flexibility and insulin resistance.” American journal of physiology-endocrinology and metabolism 295.5 (2008): E1009-E1017.

(2) Muoio, Deborah M. “Metabolic inflexibility: when mitochondrial indecision leads to metabolic gridlock.” Cell 159.6 (2014): 1253-1262.

(3) Rynders, Corey A., et al. “Sedentary behaviour is a key determinant of metabolic inflexibility.” The Journal of physiology 596.8 (2018): 1319-1330.

About the Author:

Dr. Becky Gillaspy, DC graduated Summa Cum Laude with research honors from Palmer College of Chiropractic in 1991. 

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