The Beginner’s Guide To Metabolic Flexibility (And 5 Ways to Boost It)
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The Beginner’s Guide To Metabolic Flexibility (And 5 Ways to Boost It)

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The Beginner’s Guide To Metabolic Flexibility (And 5 Ways to Boost It)

Posted a year ago

Brian Stanton

Brian Stanton


Dr. Kevin R. Gendreau

Dr. Kevin R. Gendreau

Author and Scientific Reviewer

Expert Approved

If you’re seeking health, you’re seeking metabolic flexibility. The goals are synonymous. 

When you’re metabolically flexible, your body oscillates smoothly between burning fat and burning carbs. During your pre-breakfast morning jog, you burn fat. And after a mixed dinner, you shift over to carbohydrate metabolism—but not for long. 

Why do you think athletes stay so lean despite massive caloric intakes? All the exercise makes them the metabolic equivalent of Gumby after a month-long yoga retreat. 

But you don’t need to be a pro athlete to benefit. Keep reading to learn about increasing metabolic flexibility, tracking progress, and reaping the rewards of better metabolic health

What Is Metabolic Flexibility?

Metabolic health refers to how you use, partition, and store energy. It’s generally assessed by blood sugar levels, with higher fasting blood sugar denoting worse metabolic health. 

Metabolic flexibility is a subset of metabolic health. The more metabolically flexible you are, the better you swing between burning fat and burning sugar. An example will help illustrate. 

A metabolically flexible person will eat carbs for dinner, burn sugar for a while, store the excess glucose as muscle glycogen, and return to burning fat in hours. A metabolically inflexible person, however, will eat that same dinner, store the excess glucose as fat, and stay in fat storage mode in the hours and days that follow.

The flexible person is a fat-burning machine. The inflexible person is a fat-storing machine. What makes their bodies behave this way?

To answer, let’s introduce insulin. 

Insulin and Metabolic Flexibility

Insulin is your master energy hormone, blood sugar boss, and fatty acid partitioner-in-chief. Insulin is a complicated hormone, but we can simplify its role in metabolic flexibility with two points[*]: 

  • High insulin levels promote fat storage
  • Low insulin levels promote fat burning

Metabolically inflexible people have high insulin levels all the time. They’re insulin resistant, meaning they need more insulin to manage their chronically-high blood sugar[*]. (Note: insulin resistance is the central pathology in type 2 diabetes—a condition of extreme metabolic inflexibility.) Some people may have a genetic predisposition to insulin resistance, but a high carb, high sugar diet most certainly worsens this problem.

Metabolically flexible people have a different relationship with insulin. Insulin goes up, stores the blood sugar in muscle cells (as glycogen rather than fat), then goes down again so fat-burning can resume. That’s how you want the machine to run. 

Why You Want to Be Metabolically Flexible

When you’re metabolically flexible, you use energy more efficiently. You burn carbs when necessary, and fat (including body fat) when not. 

Here’s how that may benefit you:

  • More stable energy. Access body fat for fuel and kiss the 4-o-clock slump goodbye.
  • Reduced cravings. Less reliance on glucose (blood sugar) for energy means fewer appetite swings. 
  • Fat loss. If you want to lose fat, it may help to increase your fat-burning capacity. 
  • Mental clarity. Burning fat produces ketones that fuel your brain with clean, efficient energy. 

But the best news is for your longevity. When you stay metabolically flexible—when you avoid type 2 diabetes—you reduce your risk of heart disease, Alzheimer’s, multiple forms of cancer, and many other chronic conditions.[*

How To Increase Metabolic Flexibility

Fostering metabolic flexibility is borne of living a healthy lifestyle. Let’s review the main areas to focus on. 

#1: Diet

High-carb, high-sugar diets are a significant driver of the current metabolic crisis in America.[*] If you can avoid sugar, you’re doing better than most. 

Beyond avoiding sugar and eating nutrient-dense whole foods, consider a Keto diet. Limiting carbs on Keto keeps insulin low and helps you stay in fat-burning mode. 

Multiple studies show that Keto boosts metabolic health in obese and diabetic populations.[*][*][*] In the Virta Health study, Keto helped 94% of 218 people with type 2 diabetes reduce or eliminate insulin therapy.[*

#2: Exercise

To keep insulin functioning well, try to be active every day. Exercise improves insulin sensitivity and, therefore, metabolic flexibility.[*

High-intensity interval training (HIIT) is an efficient way to benefit. In one study, six weeks of HIIT training (3 cycling sessions per week) improved metabolic health in older adults.[*

#3: Intermittent Fasting

Taking regular breaks from eating (intermittent fasting) helps you switch from burning sugar to burning fat for energy.

The mechanism is simple. By compressing your feeding window, you suppress insulin for more of the day.[*] With time, your body’s insulin sensitivity improves. Less insulin, more fat burning. 

#4: Sleep

Are you sleeping seven to nine hours per night? If not, you’re not maximizing your insulin sensitivity and fat-burning capacity.[*

Short sleep also increases hunger hormones.[*] That’s not helpful if you’re trying to avoid the brownies your unhelpful colleague baked for the office. 

#5: Stress reduction

When you’re stressed, you secrete the hormone cortisol. Cortisol then elevates blood sugar and suppresses fat burning as part of the “fight or flight” response.[*

The extra sugar provides quick energy for fleeing a crazed hippopotamus but hampers your long-term health goals. Keep stress in check with meditation, yoga, deep breathing, email avoidance, and other time-tested relaxation methods. 

Assessing Your Metabolic Flexibility

To assess your metabolic flexibility, take a look at:

  • Your blood sugar levels (optimal fasting levels are likely below 85 mg/dL)[*]
  • Insulin levels
  • Your performance on an oral glucose tolerance test (OGTT)
  • Ketone levels (ketones are a product of fat burning, and between 0.5 and 3 mmol suggest nutritional ketosis)
  • Your energy levels between meals
  • Your weight management efforts
  • Your exercise performance in the fed vs. fasted state 

And for real-time feedback on your metabolic flexibility, check out a new device called Lumen. Lumen measures metabolites on your breath to determine whether you’re burning fat or carbs for energy. Pretty cool. 

Tracking Metrics for a Healthier Metabolism

If metabolic flexibility is the big hairy goal, what small, achievable steps should you take to reach it? In other words, what micro goals will lead to your desired result? 

Simple. The micro goals should relate to the metabolic health boosters we talked about earlier: diet, sleep, intermittent fasting, stress reduction, and exercise. 

That’s where Carb Manager comes in. With Carb Manager, you can:

  • Track macros and log meals to reduce your carb or calorie intake
  • Optimize your fasting routine with our IF tracker
  • Stay accountable by logging exercise and syncing your favorite fitness devices
  • Prioritize sleep with our sleep tracking system
  • And much more

Keep improving your routine, and you’ll keep improving your metabolic flexibility. Your long-term health will appreciate it.

Disclaimer: This article contains affiliate links. Carb Manager may earn a commission for qualifying purchases made through these links.

Comments 3

  • BlithesomeKetone530079

    BlithesomeKetone530079 a year ago

    If I switch to IF, do I still consume the suggested calories & macros?

    • GrammyBev49

      GrammyBev49 a year ago

      ✔️ I’m working on lowering insulin resistance (not diabetic) with my nutritionist & PCP. Good explanations and recommendations in this article.

      • SuperCauliflower664721

        SuperCauliflower664721 a year ago

        This really works!