|March 3, 2022

What is Metabolic Flexibility and How Can You Achieve It?

By Courtney Sperlazza, MPH
Reviewed by Emily Gonzalez, ND for Scientific Accuracy

What is Metabolic Flexibility and How Can You Achieve It?

  • Being in ketosis is great for your brain and your waistline, but there’s another state that’s even better for long-term health: metabolic flexibility.
  • Metabolic flexibility means your body can use whatever fuel is available, whether that’s carbs or fat.
  • Your body’s ability to switch between different fuel sources can help support sustained energy production, fewer blood sugar roller coasters, fewer cravings and improved fat-burning.
  • If you need to eat every few hours to keep from getting hungry, grumpy and distracted, this article is for you.

Being flexible comes in handy in all sorts of situations. Bad weather keeping you from your morning run outside? No problem, head to the gym instead. Favorite coffee shop closed? Make your own Bulletproof Coffee at home. Took a wrong turn while driving? Simply find another route.

Your body’s metabolism benefits from being flexible, too. Rather than only being able to use carbohydrates or fat for energy, a flexible metabolism can switch between both with ease. This state is called metabolic flexibility, and there are a host of different reasons why improving your ability to utilize multiple fuel sources can help support your overall health and wellness.

Keep reading to find out what messes with metabolic flexibility and how to get back into a state where you can burn through your calorie supply, no matter where it comes from.

What is metabolic flexibility?


As the name suggests, metabolic flexibility means that your body’s metabolism is flexible and can use whatever fuel is available to it, whether that’s fuel from food or fuel already stored in your body. If you’ve eaten a snack or a meal recently, your body will metabolize that food and use it for energy production. But if it’s been a while since you last ate, your metabolism can switch over to burning fuel that’s already in your body, like fat and sugar stores. Scientists refer to these fuel-burning processes as fat oxidation and glucose oxidation.

In pre-industrial times, before we had restaurants and grocery stores, humans were metabolically flexible by necessity. Some days there was plenty of food, and other days there wasn’t enough to go around. Metabolic flexibility allowed people to go days without eating and feel fine. The same is true, to some degree, in our modern society, such as when we’re doing high-intensity exercise or have high levels of energy expenditure throughout the day—our bodies need to adapt and use the right amount of fuel, depending on the situation.

Benefits of metabolic flexibility

Metabolic flexibility benefits are similar to intermittent fasting and keto benefits: sustained energy, fewer blood sugar roller coasters, fewer cravings and improved fat-burning.

When you’re metabolically flexible, your body doesn’t have to keep your food-seeking mechanisms constantly “on.” Instead, your body is able to burn whatever fuel is available, seamlessly shifting from one fuel source to another—without you even noticing.

Two factors that lead to metabolic inflexibility

a basket of dinner rolls on a table

Your body is wired for metabolic flexibility. Today, a lot of things disrupt metabolic flexibility—and can actually lead to metabolic inflexibility—including a modern diet and metabolic disorders like insulin resistance or type 2 diabetes.

The Standard American Diet or any diet high in carbs

The standard American diet emphasizes eating carbs and eating frequently—at minimum, three meals a day plus snacks to carry you in between.

Eating this way accustoms your body to look for carbs for energy. When carbs go missing, your body clamors for them, and you end up with fatigue, cravings and distraction until you can refuel. Taken together, this can lead to weight gain in some individuals.

Insulin resistance

insulin and Intermittent fasting_Insulin resistance tests

Insulin resistance is what happens when you eat carbs and your cells do not open up to receive the resulting fuel. A high-carb diet can lead to insulin resistance because frequent surges of insulin have a desensitizing effect.

Being insulin-resistant, which can be a precursor to type 2 diabetes and sometimes occurs in obese individuals, includes symptoms like feeling extremely hungry or thirsty, frequent urination, tingling hands and feet, fatigue and frequent infections. You can help stave off insulin resistance and improve your insulin sensitivity with steps like eating a low-carb diet or incorporating intermittent fasting into your lifestyle.

How to become metabolically flexible

A person seasoning steak with Bulletproof products for cooking

Curious about how to become metabolically flexible? You don’t need to take drastic steps overnight, but you may need to shift what you eat and when you eat to encourage flexibility in your body’s fat metabolism and glucose metabolism.

As with any dietary change, be sure to consult with a doctor or nutritionist first, and be sure to mention any family history of obesity, cardiovascular disease and diabetes (or pre-diabetic diagnosis). And remember: There’s no one-size-fits-all approach to health and well-being. We all have different body compositions, body masses, body weights, metabolic rates and other factors that come into play.

Adopt a ketogenic diet

Salmon and other ketogenic foods

One way to improve metabolic health and flexibility is to adopt a ketogenic diet, which means eating a low-carb, high-fat diet. When your body is in ketosis, it starts to burn fat for energy and produce ketones. In this ketogenic state, your metabolism more readily burns dietary and stored body fat for energy.

Keto will help you transition to burning fat for fuel, but your first go-around can be tough thanks to the keto flu, during which you may feel tired, irritable, hungry or even have full-blown flu-like symptoms like headaches or body aches.

Cyclical keto is a great way to experiment with metabolic flexibility because you cycle between lower-carb and higher-carb days. Cyclical ketosis involves eating an extra serving of carbs once a week for two main reasons: first, to maintain the ability to digest them, and second, because your body needs them for some key processes. With cyclical ketosis, you’ll have a higher carb day (over 100g of carbs) once a week.

Intermittent fasting for metabolic flexibility

It’s a popular practice to do an extended fast to achieve metabolic flexibility, but intermittent fasting, which is restricting food for a period each day—usually 12-18 hours—is a good way to address insulin resistance.

Intermittent fasting allows you to burn enough fat to use for energy, while releasing a level of toxins that your body can handle.

Intermittent fasting plus cyclical ketosis is one of the fastest ways to increase metabolic flexibility. It gets your body used to using the fuel that’s available, and your system won’t go into a panic whenever one fuel selection (glucose, glycogen or fat) isn’t available.

The bottom line: Metabolic flexibility is proof positive that diets aren’t one-size-fits-all and there are benefits to phasing between different styles of eating to support your overall health. As always, be sure to incorporate the pillars of a healthy lifestyle, too, such as exercise training and physical activity, eating nutrient-rich whole foods, drinking water and managing stress.

Want to learn more about intermittent fasting? Check out these types of fasting diets (and how to choose the right one).

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