What is Metabolic Flexibility and Why Does It Matter?

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Metabolic flexibility is best described as the ease at which your body can burn either carbs or fat for fuel. Both carbs and fats are fantastic energy sources to fuel our daily tasks and workouts, and we’re almost always burning a little bit of both at the same time. But how easily your body switches from one to the other is highly correlated with being lean and healthy!

The relationship is so strong that I believe metabolic flexibility is a major key in getting the results you want if you’re looking for a lean, strong body.

Our brain and muscles preferential burn glucose (carbs) for fuel. If you want more information on how and why, check out this old post “Carbs vs Fat: How Our Bodies Use Energy”. Also - fair warning - I’m going to oversimplify our bodies energy processes in this article (like, a lot) so I can get the main point across.

Most of the time, when we are at rest, our body should primarily be burning fat and using the oxidative energy cycles. But sometimes our hormones are a bit funky and we’re not so good at burning fat for fuel.

  • Do you ever skip a meal and get MAJORLY hangry?

  • If you eat a high carb/sugar meal do you experience a major crash later?

This might signal a not so great relationship between your body and carbs, where we are dependent on carbs coming in, but also not great at handling high levels of carbohydrate.

How do we make this better?

We help our body get better at burning fat for fuel. And luckily, it’s not so hard to do!

One of the BIG things that effects our bodies ability to utilizes fats vs carbs is STRESS.

(Eye roll. Of course. You knew this would be in here. Stress is just so darn pervasive!)

High stress (whether good stress or bad stress) drives up our heart rate, it drops our heart rate variability, and both of those things mean we end up burning more glucose (carbs). When we are under stress our body releases carbs from our storage systems so it’s ready to use if we need to fight or flee. The problem is, very little of our stress ends with large physical demands these days. So we’re left with a whole bunch of glucose circulating in our blood stream with no real job to do. It either has to be put back into the liver, pulled into the muscles, or stored some other way (possibly as body fat).

If you’ve got all this sugar floating around your body isn’t going to be transitioning into fat burning as much, because why would it? It’s got the faster, easier option sitting right there! Carbs galore!

What’s another thing that impacts our metabolic flexibility? SLEEP.


Not getting enough sleep is a stressor. This is likely a large reason why we see the effect sleep has on our metabolic flexibility. Interestingly, lack of sleep plays a large role in our bodies ability to “down regulate” into fat oxidation (fat burning) through insulin disruption. Basically, if you're under slept your body will burn more carbs for fuel. This is true whether you’ve gotten too few hours of sleep OR if your sleep has been fractured and interrupted (hello, new parents with tiny babies waking you up every hour or two… I’m talking to you!)

Messed up sleep means poorer glucose regulation, decreased leptin levels and increased ghrelin levels. In English, that means you’re more likely to experience blood sugar roller coasters, less satiety from your food, and increased appetite. That makes you more likely to experience cravings, more likely to give in to those cravings, and more likely yo overeat in general. All just from lack of sleep!

I know, I know… you want fancy exercises and special diets and the next big thing in fitness. I WISH I could give you that stuff with a clear conscious. But it just doesn’t work that way. Turns out stress management and getting enough quality sleep are some of the best tools in our tool belt above and beyond eating appropriately and working out moderately often. Here’s the plus side though - they are both FREE! You just have to do it. This is where we go back to one of my BIG training principles. Consistency is KEY. Consistency will beat out talent. It will beat out effort. It will beat out every single fad diet out there. Consistency will bring you the results you want. Period.

So, how do you work on increasing YOUR metabolic flexibility and restoring your body’s natural balance between burning carbs and fats?

  1. Have a workout plan that maximizes metabolic flexibility.

    • You should be training all three energy systems so you’re effectively able to use and shift between different types of fuel.

    • You should be building muscle because it is the best way to increase your ability to use carbohydrates.

  2. Manage your stress. Good stress or bad stress, our body has ONE stress response. Too much stress and you end up with a stress switch stuck to “on”. Your stress switch is made to be turned on and then back off.

    • My favorite way to manage stress is with 4 x 8 breathing. Breathe slowly in for 4 counts, then out for 8. Have you ever done Savasana at the end of a yoga class? It’s pretty much like that.

  3. Get enough quality sleep. You can’t control if you actually sleep. But you can control how you prepare for sleep.

    • Dim your lights early in the evening.

    • Try to cut out blue lights after the sun has gone down.

    • Watch the sun rise and set to help your circadian rhythm.

    • Make sure your room is cool and dark.

There you have it! 3 simple steps for maximum impact and results that might make the difference between feeling stuck in a plateau or continuing on your journey!

Have a question? ! I’d love to hear from you by email at Ashley@AshleyBrownFitnessNutrition.com OR on Instagram at @ashleybrownfitnessnutrition.

NutritionAshley Brown