Metabolic Flexibility- YOU WANT IT!

January 27, 2017

Does anyone else out there feel like they have a lot of fuel stored as fat on their bodies? Most of us would love to be able to access our fat stores and burn them in our sleep, and throughout the day when we get hangry!

In an ideal world we could go days without food, and our bodies would become fat burning machines!

For most people though, that is not the case. They cannot seamlessly move through their day without the sensation of being ‘hangry’ or a NEED for food. Most North Americans are metabolically inflexible.


Metabolic flexibility is essentially a fancy way of saying that you have the ability to switch between using fat and sugar throughout the day and night.1


Sugar-Burner or Fat-Burner?

Carbohydrates, or sugars, are the easiest source of fuel for our bodies, and therefore they tend to be used first. In scientific experiments when you increase the amount of carbohydrates consumed it will increase the amount of carbohydrate that your body uses as fuel, AND it also suppresses the ability to use fat. This is partially due to the insulin response. When fat is consumed as the primary source of fuel though, the response is not as predictable.

The ability to use fat as fuel is different depending on your current state of metabolic health, if you are insulin resistant, if you have a family history of diabetes, or for other genetic reasons. This is why some people get the ‘low carb flu’ or feel unwell the first few weeks of a low carb diet. These people cannot use fat as fuel efficiently.

Even in those who can easily use fat as fuel the process of acclimation to this new fuel source can take time. You will see a slow increase in fat usage and a slow decrease in carbohydrates dependency.


What causes metabolic inflexibility? AKA The inability to burn fat as fuel.

Genetics: Those with a family history of diabetes tend to have a higher insulin response when they consume carbohydrates. Insulin is a fat storage hormone and shuts down your ability to use fat as fuel.

Insulin resistance: When you are insulin resistant it essentially means that your body is not listening to the instructions of insulin, which is telling you to lower your blood sugar and store it away as fat. It’s like a child, after they don’t listen for a while you have to start yelling! You begin to create more and more insulin in response to carbohydrates in order to keep your blood glucose levels down1.

Decreased mitochondrial function: The mitochondria are our energy producing powerhouses, and they are involved in the fuel selection in our bodies. When the mitochondria are not working properly due to inflammation, oxidative stress, toxicity etc then they can contribute to insulin resistance AND metabolic inflexibility which can have a coumpound effect.

Inactivity and improper fat storage: When fat is stored in the muscles and not properly disposed of through exercise and metabolic compensation, then it can cause a whole host of problems2!


Signs that you are metabolically inflexible.

You may be metabolically inflexible if the following characteristics sound familiar to you:

  • You carry weight around your abdomen
  • You gain weight easily and struggle to lose
  • You get hangry or shaking often, but still don’t lose weight
  • You can’t go more than a few hours without eating
  • You feel ill on a low carbohydrate diet even though you think it would help you.


You are metabolically inflexible! Now what?

Action steps

  1. Keeping insulin low in the AM. Eating a higher fat, moderate protein and low carbohydrate breakfast can help to decrease your bodies tendency to be a Sugar Burner all day long.
  2. Lift heavy things. This is critical to producing more mitochondria, improving the ones you have and increasing insulin sensitivity. Exercise is not about burning calories, it is about hormonal changes. Weight lifting and high intensity interval training contribute to that positive hormonal balance.
  • Eat the good fats. MCT, coconut, avocado and olive oil are all anti-inflammatory fats that have a minimal effect on insulin and can help to promote proper mitochondrial function. Win-Win.



  • Metabolic flexibility is the ability to switch back and forth between sugar burning and fat burning.
  • Insulin resistance is highly correlated with metabolic inflexibility because it prevents increases your reliance on sugar for fuel. (Leaving your fat cells sitting there quite comfortably!) 1
  • Mitochondrial function (your energy powerhouses) seem to be highly involved with metabolic flexibility. Exercise can help to improve this.2
  • You cannot low carb your way into metabolic flexibility without exercise and mitochondrial performance or else you might feel quite ill/hangry/stressed in the process.


Next Stop on the Fat Loss Formula?

That is all for today. The next stop on your fat loss formula will be to investigate your inflammation levels. If you find yourself with aches, pains and allergies or food sensitivities, then this next week is a can’t miss section for you!



  1. Galgani, J. E., Moro, C. & Ravussin, E. Metabolic flexibility and insulin resistance. American Journal of Physiology - Endocrinology and Metabolism 295, E1009–17 (2008).
  2. Dube, J. J. et al. Effects of acute lipid overload on skeletal muscle insulin resistance, metabolic flexibility, and mitochondrial performance. Am. J. Physiol. Endocrinol. Metab. 307, E1117–24 (2014).

Dr. Sarah Wilson is a Naturopathic Doctor in Toronto, Ontario. Having overcome her own metabolic challenges Dr. Sarah uses her personal experience and knowledge of the latest research to help you achieve food freedom and the fat loss (and health) that you desire. She works with patients locally, and on Skype, to improve their metabolism, balance their hormones and improve their energy. Find out more at or on Facebook (

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