Posted on: January 12, 2018 at 5:11 pm

“Metabolic flexibility is the ability for your body to quickly switch back and forth between fat and carbs, efficiently using whatever fuel sources you throw at it,” explains Inigo San Millan, physiologist and director of Sports Performance Program research at the University of Colorado.  (1)

He’s talking about your body’s ability to either burn carbs (ie sugar) as energy, or burn fat stored in your body. You may already be familiar with the idea if you’ve heard about the ketogenic diet:

“In normal circumstances, the body’s cells use glucose as their primary form of energy. Glucose is typically derived from dietary carbohydrates, including:

  • sugar – such as fruits and milk or yogurt
  • starchy foods – such as bread and pasta

The body breaks these down into simple sugars. Glucose can either be used to fuel the body or be stored in the liver and muscles as glycogen.

If there is not enough glucose available to meet energy demands, the body will adopt an alternative strategy in order to meet those needs. Specifically, the body begins to break down fat stores to provide glucose from triglycerides.

Ketones are a by-product of this process.

Ketones are acids that build up in the blood and are eliminated in urine. In small amounts, they serve to indicate that the body is breaking down fat, but high levels of ketones can poison the body, leading to a process called ketoacidosis.

Ketosis describes the metabolic state whereby the body converts fat stores into energy, releasing ketones in the process.”

James McIntosh 

But new research led by San Millan’s team reveals there’s more than meets the eye when it comes to your metabolism and weight loss. The key is in your body’s ability to actually switch from regular metabolism to ketosis if it needs to. 

“As we become sedentary and physically inactive, our mitochondria become atrophied or dysfunctional, and they start losing the ability to burn glucose and fat,” San Millan said. “That’s when we become metabolically inflexible.” (1)

Keep Reading: Ketogenic Diet 101


3 Big Red Flags Your Metabolism Is No Longer Flexible:

  • sluggishness
  • stubborn extra weight
  • elevated blood sugar levels

The team at the University of Colorado Sports Medicine and Performance Center hope to bring the diagnostic tools they’ve developed to the public this year. By monitoring a person’s breathing while on a treadmill or exercise bike, they can more accurately determine how their body is metabolizing fat and carbs into expendable energy.

“There’s a misconception out there that people believe the only way to exercise is high intensity,” San Millan said. “We know that’s totally wrong. It’s not sustainable. The main thing in an exercise program is to create sustainability.”

“Sixty minutes of activity used to be nothing when we were kids. You were lazy if you only moved for an hour a day. Now, that’s a major goal.”

Keep Reading: Health Benefits of Walking

So, Does San Millan’s “Prescription” Work?

34-year-old Denver resident, Liz Wolfert signed up for the program when she was told she was pre-diabetic. And this in spite of participating in Kung Fu, climbing, races, and cycling. Liz couldn’t understand why her activities weren’t enough to reverse her condition (though she wasn’t being active consistently).

San Millan prescribed an hour of daily walking. One year later, Liz had no signs of being at risk of diabetes.


“It’s so interesting,” Liz told reporters. “I had climbed fourteeners before, but I remember how hard it was. After I started walking more, I climbed another one, and it was so much easier. It was like my body was working so much more efficiently. I started to run, and it wasn’t an excruciating process. My body has just been better primed.”

The Missing Link Between The Keto Diet and Exercise

Many people have studied the unique health benefits derived from following a “ketogenic diet” (ie reducing the intake of sugars and carbohydrates and replacing them with a variety of healthy fats instead), but San Millan’s research helps us to understand why it doesn’t work for everyone.


If a sedentary lifestyle has already negatively affected your body’s ability to metabolize fat in the first place (or more specifically, ketones), then reducing its primary source of energy will more likely leave you feeling drained and hungry.

In general, healthy weight loss must start with healthy and sustainable changes to your diet- switching from the standard American diet of salty, fried, processed foods to a variety of whole foods that mostly come from plants- that’s what really helps your body shed the extra pounds, not spending hours in a gym.

That being said, this research is evidence that adding the simple habit of walking every single day will reinforce your efforts to change your diet and help you see the results you’re looking for.

Keep Reading: 7 Weight Loss Myths You Need To Stop Believing ASAP

The Hearty Soul
Health Network
We believe in using natural ingredients to be as healthy as possible. We believe dieting will never work as well as a lifestyle of healthy habits will. We believe you can treat pain and disease without relying on addictive drugs. We believe being happy is a big part of a healthy life.

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