What Is Metabolic Flexibility? Why You Need and Want It

Want to know more about metabolic flexibility and impaired metabolic flexibility? Read on for explanations of both.

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by
Sabrina Tillman
— Signos
Health & Fitness Writer
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Reviewed by

Sabrina Tillman
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Updated by

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Science-based and reviewed

Published:
May 20, 2024
August 10, 2021
— Updated:
February 20, 2024

Table of Contents

We all know that person who can eat velvety twirls of pasta carbonara, gooey cinnamon rolls dripping with vanilla icing, and gargantuan burritos stuffed with guacamole, fries, and steak but never seems to gain weight. Rather than throw green monster side-eye shade at them, consider why this can happen. It's likely because that person has metabolic flexibility.

They may be young and sporty with a “fast” metabolism.  Or maybe they’re a long-distance runner who eats calorically dense foods to fuel their demanding training schedule. But what explains this concept from a physiological perspective?

Metabolic flexibility (different from metabolic adaptation) refers to your body's ability to adapt and utilize available fuel sources based on demand. A metabolically flexible person can switch between burning carbs or using fat as an energy source to fuel everyday tasks, exercise, or merely to think and breathe.\

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What Is Metabolic Flexibility?

At its core, metabolic flexibility is all about how your body efficiently switches between different energy sources. Think of it like a fuel switch - your metabolism can easily transition from burning carbs to fat oxidation (using fat for energy), depending on what your body needs and what nutrients are available. This adaptability is critical for important metabolic processes like regulating blood sugar levels and maintaining energy balance.

On the other hand, impaired metabolic flexibility means that your body has difficulty shifting from one energy source to another. Unfortunately, the combination of high-calorie, ultra-processed foods with a sedentary lifestyle may adversely impact metabolic flexibility. Someone considered metabolically inflexible may be unable to switch to fat-burning like metabolically flexible people. Over time, this impairment may increase the risk of fat storage, insulin resistance, diabetes mellitus, cardiovascular disease, and metabolic syndrome.

The Basics of Metabolism 

Metabolism refers to the chemical reactions your body uses to break down food into smaller substrates and turn it into energy for your cells (energy metabolism). Excess energy is stored as glycogen (a form of glucose) or in adipose tissue (fat).

Your body is in a constant balance of catabolism and anabolism. Catabolism means the breakdown of more complex molecules into smaller substances that your body can use; think lipolysis (fat breakdown) or glucose oxidation (where sugar from your food is broken down into adenosine triphosphate (ATP), the energy-carrying molecule your cells use for energy.

Anabolism does the opposite: the body uses smaller molecules to make more complex molecules and metabolites─think protein synthesis. Catabolism provides energy for the body, and anabolism requires energy.

Metabolic processes require energy, and we can measure how much your body uses with the basal metabolic rate (BMR). BMR plays a crucial role in weight management and overall health. Those with a higher BMR have a higher daily energy expenditure and burn more calories even at rest. Body size, composition, age, gender, and genetics influence your BMR, but lifestyle choices like exercise, diet, and sleep also make a difference.

What Does Metabolic Health Mean?

Metabolic health means having the ability to break down food efficiently, balance energy intake and expenditure, and adapt to different levels of physical activity or diet changes. 

When metabolic processes aren’t working as they should, it can adversely impact your health, causing weight gain, high blood sugar levels (hyperglycemia), high blood lipids (triglycerides and LDL cholesterol), low HDL (good) cholesterol levels, and high blood pressure. These are all symptoms of metabolic syndrome, a cluster of conditions that increase the risk of metabolic diseases like obesity, type 2 diabetes, heart disease, and stroke.

Optimizing metabolic health is like keeping your car engine running smoothly. Just as regular maintenance and optimal fuel selection can keep your car in good condition, taking care of your body's metabolism through healthy lifestyle choices can promote healthy aging and long-term wellness.

Metabolic Health Versus Metabolic Flexibility

Metabolic health and metabolic flexibility are related but aren’t the same thing. Metabolic flexibility is a subset of metabolic health. A person in good metabolic health may also have optimal metabolic flexibility, but it’s possible to have one without the other.

While metabolic health denotes a stable status of the biochemical processes in your body, metabolic flexibility speaks to the body's ability to switch between glucose metabolism and fat oxidation without disruption. Think of metabolic health as the destination and metabolic flexibility as the ability to quickly and efficiently navigate different routes to get there.

Why Do You Need Metabolic Flexibility? 3 Primary Benefits

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Metabolic flexibility is a state to strive for as a sign of a healthy, high-functioning body. Enjoying roasted chickpeas on a salad or sinking your fork into a puddle of mashed sweet potatoes and using the glucose to power an evening walk should be the goal. Whether you’re following a high-fat diet, a Mediterranean diet, or anything in between, here are some benefits of being metabolically flexible.

Metabolically Flexible People Can Tap into Different Fuel Sources

Metabolic flexibility allows you to use different fuel sources to power activity without difficulty. Going for a morning run? That mushroom farro you ate for dinner last night will provide the glucose you need. Don’t have time to eat breakfast and don’t feel hungry anyway? No problem. You can use stored glucose or fat breakdown to fuel your activities until you get hungry and decide to eat. As an example, people who follow an intermittent fasting lifestyle attempt to use this to their advantage by using different fuel sources when fasting.

Metabolic Flexibility Implies Optimal Mitochondrial Function

Mitochondria, the powerhouses of cells, make energy for the cells from the food we eat. Mitochondrial dysfunction is shown to be a precursor to the onset of chronic diseases, indicated by the inability to match fuel preference (glucose first if available, fat second) to demand. If your mitochondria struggle to function properly, you likely store excess energy your body doesn’t burn. This difficulty in burning fat leads to weight gain, insulin resistance, and chronic health problems associated with metabolic disorders.

Metabolic Flexibility Supports a Healthy Body Weight

An older but highly referenced study found that people with obesity or type 2 diabetes showed impaired metabolic flexibility compared to lean individuals. How is this possible? Metabolic flexibility allows the body to utilize energy efficiently, making weight loss easier while reducing the likelihood of storing excess energy as body fat.1

<p class="pro-tip"><strong>Also Read: </strong><a href="what-is-metabolic-syndrome">What is Metabolic Syndrome?</a>.</p>

Is Metabolic Flexibility the Key to Stable Blood Sugar?

Metabolic flexibility has a direct role in maintaining glucose homeostasis. The body's ability to switch between burning glucose and fat for energy can help limit spikes and dips in blood sugar, essential for overall metabolic health. 

Metabolic Flexibility Can Enhance Energy Utilization

Metabolic flexibility allows the body to switch fuel sources efficiently, which helps maintain a consistent energy supply and balance blood sugar levels. Oppositely, metabolic inflexibility may drive low energy levels by preventing the body from utilizing alternative fuel sources when glucose is unavailable.2

Metabolic Flexibility Decreases the Risk of Insulin Resistance

Insulin resistance occurs when cells become less responsive to insulin signals. Insulin is the hormone that helps lower blood sugar. With insulin resistance, the cell receptors ignore the signal to move sugar out of the blood and into the cells. Despite increasing insulin secretion, insulin levels and blood sugar remain high, impacting metabolic health and increasing the risk of type 2 diabetes. Metabolic flexibility helps to counter this resistance by allowing cells to utilize fuel without causing abnormal elevations in blood sugar levels.1

Metabolic Inflexibility Side Effects

The inability to switch between fuel sources can lead to negative side effects, including fatigue, weight gain, and unstable blood sugar levels. When the body can’t optimize fatty acid oxidation (fat breakdown), it can contribute to weight gain, as it struggles to regulate energy and store excess glucose as fat.1

How to Achieve and Improve Metabolic Flexibility

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Achieving and maintaining metabolic flexibility is not solely a matter of addressing the symptoms; it hinges on cultivating good habits that lay the foundation for overall health and well-being. These habits act as building blocks for a body that adapts, functions optimally, and resists disease processes. 

To enhance metabolic flexibility, consider integrating the following practices into your daily routine:

  • Incorporate Interval Training: High-intensity interval training (HIIT) challenges the body by alternating between high and low-intensity exercise, promoting more efficient energy usage and improving insulin sensitivity. Exercise training also supports mitochondrial content or volume, one way to measure cellular health in research.
  • Favor Whole Foods Over Processed: A diet abundant in whole foods such as vegetables, fruits, lean proteins, and healthy fats provides balanced fuel sources for the body to metabolize.
  • Keep Tabs on Glucose Levels: Monitoring glucose levels can provide valuable insights into how your body responds to diet and lifestyle choices.
  • Adjust Macronutrient Intake: Personalizing your intake of carbohydrates, fats, and proteins can aid your body in becoming more adept at switching between fuel sources.
  • Prioritize Sleep: Quality sleep is essential for regulating hormones that affect metabolism, including those that help manage blood glucose levels.
  • Stay Hydrated: Proper hydration is crucial for metabolic processes, and even mild dehydration can negatively impact your body's ability to manage energy.

The Importance of Monitoring Glucose Levels for Metabolic Flexibility

Using the Signos app with a Continuous Glucose Monitor (CGM) can transform how you track and understand your blood sugar levels. The Signos app is a powerful tool to help you make real-time data-driven decisions, giving you personalized insights and actionable feedback. 

There’s a lot of variability in how each person responds to diet and lifestyle habits. With Signos, you can see how your blood sugar responds to foods and the effects of exercise so you can adjust your lifestyle habits to optimize whole-body health.

<p class="pro-tip"><strong>Learn More: </strong><a href="metabolic-syndrome-diet">A Metabolic Syndrome Guide: Diet, Foods to Eat/Avoid + Tips</a>.</p>

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References

  1. Smith, R. L., Soeters, M. R., Wüst, R. C. I., & Houtkooper, R. H. (2018). Metabolic Flexibility as an Adaptation to Energy Resources and Requirements in Health and Disease. Endocrine reviews, 39(4), 489–517. https://doi.org/10.1210/er.2017-00211
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  6. Kelley, D. E., Goodpaster, B., Wing, R. R., & Simoneau, J. A. (1999). Skeletal muscle fatty acid metabolism in association with insulin resistance, obesity, and weight loss. The American journal of physiology, 277(6), E1130–E1141. https://doi.org/10.1152/ajpendo.1999.277.6.E1130
  7. Galgani, J. E., Moro, C., & Ravussin, E. (2008). Metabolic flexibility and insulin resistance. Am j physiol. Endocrinology and metabolism, 295(5), E1009–E1017. https://doi.org/10.1152/ajpendo.90558.2008
  8. de Souza, J. F. T., Dáttilo, M., de Mello, M. T., Tufik, S., & Antunes, H. K. M. (2017). High-Intensity Interval Training Attenuates Insulin Resistance Induced by Sleep Deprivation in Healthy Males. Frontiers in physiology, 8, 992. https://doi.org/10.3389/fphys.2017.00992
  9. Larsen, S., Nielsen, J., Hansen, C. N., Nielsen, L. B., Wibrand, F., Stride, N., Schroder, H. D., Boushel, R., Helge, J. W., Dela, F., & Hey-Mogensen, M. (2012). Biomarkers of mitochondrial content in skeletal muscle of healthy young human subjects. The Journal of physiology, 590(14), 3349–3360. https://doi.org/10.1113/jphysiol.2012.230185
  10. Tiwari, R., Tam, D. N. H., Shah, J., Moriyama, M., Varney, J., & Huy, N. T. (2021). Effects of sleep intervention on glucose control: A narrative review of clinical evidence. Primary care diabetes, 15(4), 635–641. https://doi.org/10.1016/j.pcd.2021.04.003

About the author

Sabrina has more than 20 years of experience writing, editing, and leading content teams in health, fitness, nutrition, and wellness. She is the former managing editor at MyFitnessPal.

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Please note: The Signos team is committed to sharing insightful and actionable health articles that are backed by scientific research, supported by expert reviews, and vetted by experienced health editors. The Signos blog is not intended to diagnose, treat, cure or prevent any disease. If you have or suspect you have a medical problem, promptly contact your professional healthcare provider. Read more about our editorial process and content philosophy here.

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