Metabolic Flexibility: What It Is, Why It Matters, and How to Improve It

Flexibility makes everything easier, whether we’re talking about joint flexibility or mental ability or pretty much anything else.

But your joints aren’t the only thing that benefits from being flexible. Your body’s metabolism and mitochondria do, too!

Keep reading to learn why metabolic flexibility — aka a person’s ability to metabolize various energy sources for fuel — is so important.

• What is metabolic flexibility?
• Metabolic flexibility vs. metabolic syndrome
• Why we need metabolic flexibility to thrive
• Does metabolic flexibility help you lose weight?
• How to regain your metabolic flexibility
• Why fasting helps foster metabolic flexibility
  
  

What is metabolic flexibility?

Metabolic flexibility simply refers to having an ability to process whatever fuel we consume into energy. Intuitive enough, right?

Think of it this way: most cars run off 91-octane gasoline. Many sports cars run off premium gas. And a good amount of trucks run off diesel. But a select few safari trucks can run off both gasoline and kerosene.

The human body is equally oriented toward survival. For most of human history we simply didn’t have steady access to safe, calorie-dense food. There was a time when we were either hunting down large game, scavenging for berries, or fasting — with not much in-between.

Even just a few hundred years ago, the average person was well-acquainted with occasionally going days or weeks without food.

Suffice to say that the human body evolved with metabolic flexibility in mind. We can run off of sugars (glucose, fructose), fatty acids, ketones, ketone esters, ethanol, and numerous other food sources.We can even convert carbohydrates into fats, and proteins into carbohydrates when other macronutrients aren’t available.

Healthy, metabolically flexible people can switch from burning fat one minute to burning glucose the next. They can also cycle into a ketogenic state when food isn’t around. Their blood sugar also remains under control, sparing them from mood swings and/or out-of-control hunger (the hangry state).

Metabolic flexibility is associated with healthier mitochondria, which in turn are associated with a whole host of health benefits. People who are metabolically flexible live longer and stay healthier than those who are not. [1]

Related: Carbs vs Fats. Glucose vs Ketones.

Metabolic flexibility vs. metabolic syndrome

What’s the opposite of metabolic flexibility?

While you could call it metabolic inflexibility, most researchers instead call it metabolic syndrome.

Metabolic syndrome is marked by an increasingly poor ability to produce the blood-sugar-regulating hormone insulin. It’s also marked by insulin-resistant muscle cells and insulin-sensitive fat cells.

This combo results in poor body composition and difficulty building muscle.

If left unchecked metabolic syndrome invariably leads to type-2 diabetes and other health conditions. Unfortunately, a growing percentage of the population is falling into these categories. The most recent figures estimate that 34% of US adults have metabolic syndrome. That’s just over one in three! [2]

Image source: ResearchGate

Why’d we get here? Because a growing portion of modern humans has lost the metabolic flexibility of their ancestors. Today food is everywhere, so much so that most people rarely find themselves in a situation where they have to go hungry for long. Nor do we have to put in much work to earn a meal.

Making matters worst, the food most people eat also reduces their metabolic flexibility. That’s because these foods are typically high in processed seed oils, processed sugar, and other inflammatory substances.

Why we need metabolic flexibility to thrive

Metabolic flexibility is associated with a variety of other health benefits, including:

• Easier weight maintenance. People who are metabolically flexible have an easier time losing weight and keeping it off. They might even have a slightly higher resting metabolic rate.
  
  
• Better body composition. People who are metabolically flexible have more insulin-sensitive muscle cells, allowing the energy they take in to go into muscle cells instead of fat cells.

• Lower odds of developing metabolic disease. Metabolic flexibility practically guarantees that you’ll be able to avoid blood-sugar-related health problems. And closely regulated blood sugar is good for more than just diabetes prevention. It also reduces glycation and may slow down the aging process in the long run. [3]

• Better workout performance. Metabolic flexibility allows you to stay energized throughout long workouts without hitting the wall or ‘bonking.’

• Improved sleep patterns. Metabolic flexibility means better blood sugar control and glycogen storage throughout the night, resulting in fewer early-morning runs to the bathroom.

• Increased energy levels. Metabolic flexibility allows your body to switch back and forth between fat- and sugar-burning with ease. Fat-burning provides steady "diesel" energy, while sugar-burning generates ATP as quickly as possible.
  
  
• Better overall health. Metabolic flexibility is positively correlated with longevity, mental health and even cognitive function.
  
  

Does metabolic flexibility help you lose weight?

Yes, it sure can! Metabolic flexibility enables your body to burn fat for fuel at rest, resulting in lower fat mass.

In addition to that, the same way of eating that promotes metabolic flexibility also promotes thyroid health and hormonal health. You might find yourself getting leaner as you pursue metabolic flexibility.

How to regain your metabolic flexibility

If you’re exhibiting symptoms of metabolic syndrome, don’t panic. It’s very possible to undo the damage and regain your metabolic flexibility over time. Here’s how.

1. Correct nutrient deficiencies

Being deficient in certain nutrients can cause your body to start losing its insulin sensitivity, resulting in metabolic syndrome in the long run. Prime candidates include zinc, chromium, [4], magnesium [8] and vitamin D [9].

Cymbiotika Zinc Complex is a blend of three forms of zinc. Bioptimizers Magnesium Breakthrough is a full spectrum formula with all 7 forms of magnesium. Bulletproof A-D-K packs vitamins A (as retinyl palmitate), D3, K1 and K2.

2. Get some exercise

Working out is a sure way to improve your metabolic flexibility. Endurance exercise (think walking, hiking, gentle cycling) has been shown to improve mitochondrial health, while HIIT and other types of interval training can improve your hormonal status. [5]

3. Try fasting

Fasting is one of the fastest, most direct ways to become more metabolically flexible. Fasting essentially forces your body into fat-burning mode. More on how this works a little later.

Related: Intermittent Fasting for a Longer and Healthier Life

4. Try keto

The keto diet reduces your body’s insulin production demands almost instantly. It also retrains your metabolism to burn fat for fuel. Most people experience fast weight loss on the keto diet, too, which further improved metabolic flexibility [10].

But perhaps the very best way to apply the ketogenic diet is through cyclical ketosis. This approach involves eating a larger amount of carbs (100-200 grams) once or twice a week. While eating carbs will momentarily kick you out of ketosis, it’ll also help your body stay sensitive to hormones like T3 and leptin. [6]  
 

Why fasting helps foster metabolic flexibility

As we said above, fasting practically forces your body to burn fat for fuel. Studies hint that any type of fasting may foster metabolic flexibility, so it makes sense to opt for whichever type feels most sustainable — even enjoyable — to you.

Some of the most popular types of fasting include:

• Intermittent fasting (IF)
• Alternate day fasting
• Eat-stop-eat
• 5:2 fasting
• Dry fasting

Intermittent fasting (IF) is probably the very most popular of all these approaches. That’s because it’s so approachable. Since the "easiest" version of IF only calls for as little as a 12-hour fasting window, getting into it can be as easy as just skipping breakfast. Although, strict IF calls for a 16h fast and an 8h "eating window". This is thought to provide the greatest benefits [11].

Time-controlled fasting prevents high fat diet-induced metabolic inflexibility in skeletal muscle. 
Image source: ResearchGate

Most people opt to take things a little further by fasting for 18 hours of each 24-hour day, leading to an 8-hour eating window. That’s enough time to eat two big meals and a snack or two.

What’s particularly interesting about intermittent fasting is that not all of its benefits can be attributed to calorie restriction. Intermittent fasting may reverse metabolic syndrome even when compared to an isocaloric three-meals-a-day diet. [7]

Summing things up

Metabolic flexibility is one of the most foundational, farthest-reaching health metrics. With it you’re likely to enjoy a long, fit, mentally sharp life — without it, you’ll be far more likely to become obese, diabetic, and chronically ill.

Want to ensure that you stay metabolically healthy in the long run? Consider eating a nutrient-rich diet, partaking in exercise that you enjoy, and occasionally caloric-restriction. Your metabolism should be able to take things from there.

References:

1 - https://www.sciencedirect.com/science/article/pii/S0025619622000428
2 - https://www.heart.org/en/health-topics/metabolic-syndrome/your-risk-for-metabolic-syndrome
3 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3951818
4 - https://pubmed.ncbi.nlm.nih.gov/27854048/
5 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1540458/
6- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4251481/
7 - https://clindiabetesendo.biomedcentral.com/articles/10.1186/s40842-020-00116-1
8 - https://pubmed.ncbi.nlm.nih.gov/27834189
9 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6513299/
10 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400909/
11 - https://www.sciencedirect.com/science/article/pii/S1568163718301478?via%3Dihub