What is Metabolic Flexibility and How Can You Achieve It?

You might think that a good number on your keto meter is the gold standard of fat burning. Being in ketosis is great for your brain and your waistline, but there’s another state that’s even better for long-term health: the state of metabolic flexibility. Metabolic flexibility means your body uses whatever fuel is available – dietary fat, stored fat, or glucose (sugar), or glycogen (sugar stores).^[1]

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.

In an episode of Bulletproof Radio (iTunes), author and osteopathic physician Dr. Joseph Mercola estimates that only about 15% of the population is metabolically flexible. Today, a lot of things disrupt metabolic flexibility, including a modern diet and metabolic disorders like insulin resistance or diabetes.

If you need to eat every few hours to keep from getting hungry, grumpy, and distracted, this post is for you. 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.

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The two main things that disrupt metabolic flexibility

Your body is wired for metabolic flexibility. A lot of modern practices mess with your ability to switch between burning fat and burning sugar and carbs.

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 looking for carbs for energy. When carbs go missing, your body clamors for them, and you end up with weakness, cravings and distraction until you can refuel.

Insulin resistance

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.

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Ways to increase metabolic flexibility

When you’re metabolically flexible, you almost never get cravings or feel hangry. Metabolically flexible people tend to maintain a healthy weight without trying too hard, because your body doesn’t have to keep your food-seeking mechanisms constantly “on.” When you’re metabolically flexible, you don’t store extra fat to prepare for a constant need for energy. It burns what’s there. Sounds great, right? Here’s how to achieve metabolic flexibility.

Adopt a ketogenic diet

When your body is in ketosis and gets used to burning fat for energy, your metabolism more readily burns dietary and stored fat for energy. If you’re thinking about starting a ketogenic diet or you’ve been in ketosis, you’re probably familiar with keto flu — the first few days or weeks in ketosis that make you feel tired, irritable, hungry, or even have full-blown flu-like symptoms like headaches or body aches.

It’s not fun, but you feel incredible once you come out of it. The state of zero cravings, energy, brain power, and elevated mood that you get in ketosis is unmatched.

Cyclical ketosis for painless metabolic shifts

When you don’t eat carbs for an extended period, your body loses the enzymes and gut bacteria it needs to properly process carbs. The answer? Cyclical ketosis.

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.

Does that mean you have to start over and go through keto flu misery every week? Not necessarily. If something you eat kicks you out of ketosis for a short while and you go right back to limiting carbs, you’ll default to the fat-burning state. If you go back to pizza and cake for an extended period, you might find yourself slogging through keto flu again, but it will likely be a shorter duration of keto flu.

Once you’ve been in ketosis, it’s easier to get back into ketosis. Your metabolism becomes familiar with what happens when your glucose supply drops. Your body knows it’s not starving, so it doesn’t resist the shift. Once you’ve achieved metabolic flexibility, you can slip in and out of ketosis without the misery of keto flu.

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 better way to address insulin resistance.

Dr. Mercola cautions against the dangers of extended water fasts. He explains that your body stores fat-soluble toxins in your fat cells, to keep them away from organs where they can do damage. “When you’re doing a multiple day water fast, you are liberating these toxic chemicals. That’s all well and good unless you have too many of them, and your detoxification systems aren’t up to the challenge of biochemically modifying those toxins so that they can be essentially changed, and effective, and eliminated and excreted from your body,” he says.

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 or the other fuel type (glucose or fat) isn’t available.

As the name suggests, metabolic flexibility offers you just that — flexibility. Ultra-stringent diets lead to frustration, cravings, and failure. Flexibility allows a little bit of wiggle room and even the ability to go off the rails, and bounce back quickly.