What Is Metabolic Flexibility And Why Is It Important For Health And Performance?

You might wonder what metabolic flexibility is and how it influences health and performance.

In this article, you’ll discover everything you need to know about metabolic flexibility. And why it’s important for optimal health and performance. You’ll also get 4 practical tips to improve your own metabolic flexibility.

So if you’ve heard about metabolic flexibility, but ignored it thus far, read on to find out more.

And if you’d prefer to listen to the audio version of “What Is Metabolic Flexibility And Why Is It Important?”, click the play button below.

Defining Metabolic Flexibility

Metabolic flexibility is your ability to use the right fuel source at the right time.

The more scientific definition being, “Metabolic flexibility is the capacity for skeletal muscle to acutely shift its reliance between lipids and glucose during fasting or in response to insulin, such as in postprandial conditions.” Sparks LM et al, 2008.

Someone with good metabolic flexibility utilises carbohydrate for high intensity exercise, and switches efficiently to burning fat at low intensities, or at rest.

Conversely, metabolic inflexibility is inefficient in fuel selection. Often leading to compromised performance and health implications. For example, Type 2 Diabetes is linked to a degree of metabolic inflexibility.

In this scenario, muscle and organs become less sensitive to insulin. This causes increases in insulin production. And the down-regulation of the body’s ability to burn fat. Ultimately, creating metabolic inflexibility.

But you don’t need to fear insulin. It’s needed as part our survival. And it’s highly controllable through the diet. So think of it less as the ‘Nutritional Devil’ and more as a fuel selector switch.

So how does metabolic flexibility impact performance in the gym?

Metabolic Flexibility And Performance

A well-trained athlete is likely to have a high degree of metabolic flexibility.

To assess metabolic flexibility, we can measure the point at which carbohydrate becomes the primary fuel source for an activity. This is called the crossover point.

This crossover point occurs much later in someone who is trained. Essentially, giving them a greater capacity for exercise. And more capacity, means more power output, which means more gains.

For example, a 2017 study looking at cycling power output showed a crossover point of c.325 watts in trained subjects. And less than 200 watts in untrained.

Studies have also shown that carbohydrates are the primary fuel source for high intensity exercise. So if you want to make gains in the gym, having the ability to tap into those energy stores is advantageous.

This greater level of metabolic flexibility increases the body’s ability to handle large consumption of glucose or fat. Essentially, allowing for an efficient switch between fuel sources, depending on what’s available. Untrained athletes make this switch much slower.

So when it comes to metabolic flexibility and performance, exercise, lift weights, and do it with carbs.

Metabolic Flexibility And Health

Metabolic flexibility also has implications for health. Particularly related to the handling of nutrients following meals.

For example, a lean person with greater metabolic flexibility will be able to rapidly utilise the carbs and fat from a meal, compared to an obese person. They’re also likely to return to baseline sooner.

Metabolic flexibility also plays a role during sleep. For example, a Type 1 Diabetic, with poor metabolic flexibility may struggle to down-regulate carbohydrate use and burn fat for fuel. Likewise, someone suffering with PCOS, may preferentially burn carbohydrate and protein (muscle) during sleep. Ultimately, this could contribute to weight gain and unwanted changes in body composition.

4 Ways To Improve And Maintain Metabolic Flexibility

As you can see, metabolic flexibility is important. And plays a crucial role in health.

But it might seem like one extra headache you could do without. However, there’s good news. Because becoming more metabolically flexible doesn’t need to be complicated. In fact, the actions you need to take are simple. You may even be doing them already.

Lift Weights And Fuel With Carbs

Maintaining a healthy body fat percentage and building muscle is the first step. And these might already be your goals. So if you’re going to the gym, lifting weights, and attempting to reduce body fat through a calorie deficit, you’re on the right track.

And to help you a little more, here’s how to set up your pre and post workout nutrition.

Before training:

• 20-30g protein.
• 40-80g carbs (high GI to aid digestion).
• 30-120 minutes prior to exercise.

After training:

• 0.3g/kg protein (whey would be optimal).
• 2:1 ratio of carbs to protein (any GI).
• Carb timing not essential.

Low Intensity, Fasted Activity

Fasted cardio. Yes, it may have some benefit.

Not in terms of losing body fat. But for improving your metabolic flexibility.

Almost contrary to everything you’ve read so far, you can exercise, be healthy, and still be inefficient at using fat for fuel at low intensities. For example, a study in 2000 looking at trained cyclist, saw huge individual variability in this. With fat oxidation ranging from 23-93%.

One theory is that you can train your body to be more efficient by using fasted cardio.

But this doesn’t mean you need to be pounding the treadmill of the local gym at 4am. Instead, opt for something more achievable. A few times per week, simply go for a walk after you wake up. There’s no need to drive to the gym, warm up, or eat something specific. Just throw on your trainers and walk out the front door.

Intermittent Fasting

The benefits of fasting are often overstated and reference questionable animal research. However, fasting does have advantages. Particularly, when it comes to improving metabolic flexibility.

Periods of fasting could be used as a way to shift your Resting Metabolic Rate (RMR) to burn more fat. And this is done without compromising your ability to use carbohydrate.

But fasting isn’t for everyone. Especially if you live a stressful lifestyle. Often, it can be another complication you simply don’t need. However, if it’s an option, try it. Because it can work well for a lot of people.

And you don’t have to go cold turkey from the outset, or fast every day.

Start by aiming for a period of fasting, one day per week. And over time work up to a 19-24 hour fast.

Again, this is not going to lead to a fat loss and body composition miracle. So don’t go into it with that mentality. This is more about making small, incremental changes in your metabolic flexibility, which may or may not have an impact on body composition.

Beware Of The Keto Diet

Following a strict keto diet may impair performance and result in shitty workouts. Done for extended periods of time, you’re de-training your body’s ability to switch to carbohydrate as a fuel source. Why? Because you’re less metabolically flexible and unable to tap into those fuel reserves, as efficiently.

It’s all related to the down-regulation of the PDH enzyme. And the subsequent down-regulation of carbohydrate oxidation. Technical talk for training being a bit “meh” when you’re on a keto diet, even if you try a strategic carb-load.

Think of it like this…

There’s a truck delivering fuel to a petrol station. But on the way there, the truck itself runs out of fuel. There’s a huge amount of fuel waiting to be used, but there is no means to access it. (Analogy credit goes to Dr. Mike T Nelson).

Essentially, that’s you when you’re on a keto diet, trying to build muscle, and are having consistently crap workouts.

The Bottom Line On Metabolic Flexibility For Health And Performance

Undoubtedly, improving and maintaining metabolic flexibility is important for health and athletic performance. And while the concept may be complex, the practical actions you need to take are simple. 

Within the realms of nutrition and training, many topics appear complicated. And wrapping your head around them is a mind-fuck of seismic proportions.

But you don’t need to understand these intricacies in finite detail to make positive changes with your diet and lifestyle. In fact, in the case of metabolic flexibility, it’s as easy as 1, 2, 3, 4.

How To Improve Metabolic Flexibility

Lift weights and use carbs for fuel. Exercise will help your body select the right fuel for the job. So hit the gym and fuel higher intensity workouts with carbs.

1. Fasted Activity.
   • Fasted cardio doesn’t lead to greater fat loss. But some fasted activity could improve metabolic flexibility.
2. Intermittent Fasting.
   • Intermittent fasting is not fat loss magic. However, periods of fasting could help increase metabolic flexibility, without compromising performance.
3. Beware of the Keto diet.
   • If your goal is body composition, Keto is a valid option (assuming it suits your food preferences). But if your goal is gains, it’s probably better to stick to carbs.

What are your thoughts on metabolic flexibility? Has this article prompted you to focus on it more? Let me know in the comments below, or drop me a message on Instagram (@iron_paradise_fitness).

With Metabolic Flexibility Sorted, Here’s The Next Step In Achieving Your Fitness Goals

After reading this article, you understand the importance of metabolic flexibility for health and performance. But what about the other pieces of the puzzle? Maybe you feel my personal 1:1 coaching would help accelerate the process of achieving your fitness goals. And you’d be right!

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But for now, all I’ll say is, keep living the Lean Life. And I’ll see you soon.

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