By Dr. Nasha Winters, ND, FABNO, L.Ac.

This article highlights some points from an interview for ONCancer Health Podcast. I encourage you to also listen to the full interview here.

In my recent interview with Jason Bosley-Smith, host of the ONCancer Health Podcast, we talked about metabolic flexibility. Metabolic flexibility is a term that was first coined by Philip Randle at Oxford University. In brief, it refers to the body’s ability to shift easily between 2 different types of fuel: carbohydrates and fats. All of this happens at the mitochondrial level.

The mitochondria are the tiny organelles within every cell of your body that are responsible for producing energy. They are sometimes called “respiratory engines” or “power-houses” of the cell. Mitochondria can burn carbohydrates for fuel or fats for fuel, depending on the foods you eat and if you are full or fasting.

We are hybrid engines…

Think of your cells as hybrid-fuel vehicles. When you have metabolic flexibility, your cells and the mitochondria in your cells can easily transition between fuel sources. Unfortunately, many of us have come to rely so heavily on carbohydrates as a primary fuel source that we have lost our ability to easily switch over to burning fats. We have become metabolically inflexible.

The concept of metabolic inflexibility was introduced in 1999 by a researcher by the name of David Kelley at the University of Pittsburgh School of Medicine. He suggested that the reason cells become less efficient at burning fats as a fuel source is because of overconsumption of sugar and the presence of insulin resistance. Insulin resistance, also called pre-diabetes, is a condition that is all too common in modern times.

You will hear me describe in my interview for the ONCancer Health Podcast that a person who is metabolically flexible should be able to shift away from carbohydrate metabolism and into fat metabolism within about 12 hours of fasting. The way you can measure this is by measuring ketones in your urine.

If you fast for 12 hours overnight and do not detect ketones in your first-morning urine, you may need to allow your body a longer time to fast. Other ways to improve your body’s metabolic flexibility are to go longer periods between meals and to decrease the carbohydrates and sugars in your diet.

The reason I emphasize the importance of metabolic flexibility is because this is one foundational piece of reducing your risk of cancer. For those who already have a diagnosis of cancer, metabolic flexibility can improve their response to treatments. I talk about why metabolic flexibility matters to everyone and much more in the podcast linked below.

  Learn more by listening to the full ONCancer Health Podcast here.



Kelley DE, Goodpaster B, Wing RR, Simoneau JA. Skeletal muscle fatty acid metabolism in association with insulin resistance, obesity, and weight loss. Am J Physiol. 1999;277 (6 Pt 1):E1130-41.

Muoio DM. Metabolic inflexibility: when mitochondrial indecision leads to metabolic gridlock. Cell. 2014;159 (6):1253-1262.

Randle PJ. Regulatory interactions between lipids and carbohydrates: the glucose fatty acid cycle after 35 years. Diabetes Metab Rev. 1998;14 (4):263-283.