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Metabolic Flexibility and the Freedom of Choice

by Axel Baumann · January 27, 2020 · 4 minute read
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It is all about keeping the balance

Homeostasis is a fundamental principle in biology that represents the essence of all living organisms: the dynamic equilibrium of the body. This equilibrium allows all living beings to maintain their internal balance no matter the external conditions and is the reason why certain parameters such as blood sugar levels, body temperature, and blood pressure, among others, always remain within a certain range. When the body fails to maintain the homeostasis (e.g: high blood pressure), the complication appears (e.g: cardiovascular disease). The situation is no different when it comes to the discussion of metabolism. For this reason, the concept of metabolic flexibility is crucial to a healthy metabolism.

An evolutionary perspective 

The main predictor of survival of any species is their capacity to efficiently adapt to the environment. Energy metabolism follows the same principle of homeostasis or “balance” and according to evolutionary biology, it was developed through early human evolution in which hunter-gatherer societies had to survive in environments where they intermittently experienced long time-periods with little or no food at all. This capacity of adapting our metabolism to the sporadic food events gave us great advantages for surviving. That capacity remains relevant today, but isn’t as necessary in modern societies.

Nowadays, the context is different. According to the World Health Organization, being overweight or obese is linked to more deaths worldwide than being underweight. In fact, nutrient overload and sedentariness are two of the main contributors.

The best type of flexibility

Within our cells, energy is provided by oxidation of metabolic fuels provided by foods such as carbohydrates, lipids, and proteins, however, the rate of metabolization of these nutrients can vary significantly according to different factors, with metabolic flexibility being one of the most important ones.

Metabolic flexibility represents the body’s capacity for adapting fuel demand (fats/carbs) to fuel availability (what is in your diet).

There are 2 factors involved in this capacity:

  • How well can your metabolism switch from carbohydrates to fat oxidation (and vice versa): Individuals with great metabolic flexibility can burn carbohydrates when they eat them or can burn fats when they eat them. Contrarily, individuals that are metabolically inflexible struggle in efficiently using fats or carbs when they eat them.
  • How fast can you make this switch according to the demand: The timing for the switch is essential to understanding this concept, as it is not only related to the composition of the diet but also to the capacity of the body to adapt to the different conditions such as fasting or exercising at different intensities.

What the evidence says

Recently there has been much discussion surrounding the principle of metabolic flexibility because impaired fat oxidation during fasting, along with an impaired capacity for switching from fat to glucose oxidation (or in other words, being “metabolically inflexible”), is strongly associated with obesity, insulin-resistance, type 2 diabetes, and some types of cancer. Metabolic flexibility becomes relevant where lifestyle interventions through personalized nutrition recommendations and physical activity are considered key strategies for the prevention and as well as treatment for these conditions. 

Imagine you are able to sleep for 5 months during the cold winter without eating, drinking and you wake up leaner and more healthy. Bears during hibernation show an outstanding capacity for adapting their metabolic fuels to the demand, as they can survive long periods of time using their fat storages as the main source of energy while having an amazing capacity for preserving its muscle mass which is essential for their survival. Of course humans aren’t bears, but bears provide an example of how the principle of metabolic flexibility works.  

The path towards your goals

Metabolism in humans is complex and impacted by a variety of factors. Besides the fact that sleeping (quantity and quality) matters, increasing your metabolic flexibility requires a holistic approach. Whether you are interested in improving your energy levels, your body composition, or your health, training your metabolism to be more flexible will definitely help you to achieve your goals. Through adopting healthier lifestyle habits that are within your control, you can improve your metabolic flexibility, and thus your body’s ability to utilize the fuel you consume.


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  3. Galgani JE, Moro C, Ravussin E. Metabolic flexibility and insulin resistance. Am J Physiol Endocrinol Metab. 2008;295(5):E1009–E1017.
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  5. Rynders CA, Blanc S, DeJong N, Bessesen DH, Bergouignan A. Sedentary behaviour is a key determinant of metabolic inflexibility. J Physiol. 2018;596(8):1319–1330.
Axel Baumann

Axel Baumann

Axel has a Bachelors degree in Human Nutrition from the Universidad ISALUD, Argentina, and a Masters degree in Nutrition and Metabolism from the Universitat de Barcelona, Spain. He is also a Certified Diabetes Educator from the Sociedad Argentina de Diabetes, International Diabetes Federation.