Metabolic health isn’t necessarily a ‘state of being.’ More often than not, it’s simply a type of flexibility. When your body has the ability to respond or adapt to changes in metabolic demand (i.e., what or how much you eat), you’re said to have ‘good’ metabolic health.
There are many different ways to achieve this flexibility, ranging from low-carb diets to fasting to cutting sugar. But by far one of the simplest and most effective is adding more exercise to your routine.
So I wanted to take a moment to explain this unique connection, plus provide a few suggestions so you can start incorporating this into your own life.
First of all: a deeper dive into metabolic flexibility
Metabolic flexibility is how well your cells (aka, mitochondria) can switch between carbohydrates and fat to produce energy. The more mitochondria you have, and the larger they are, the more metabolically flexible (read: healthy) you’re likely to be.
Let’s assume, to start with, that you’re metabolically inflexible. So when you go five or more hours without eating, you may:
- Run out of easily accessible carbohydrates
- Feel tiredness, headaches, and irritability due to being low on energy
- Feel the need to eat again
Now on the flipside, let’s assume you’re metabolically flexible (aka, metabolically healthy). If you go five or more hours without eating, you may:
- Produce ketones from stored fat in your liver
- Keep your blood sugar in a healthy range without dramatic drops
- Experience minimal hunger or cravings, since your body is still running on adequate energy and doesn’t need to send out desperate signals for food
Keep in mind that metabolic flexibility also refers to how well you handle different glycemic loads.
If you’re someone who normally eats low-carb, no-sugar, high-protein meals, there’s a very good chance you can handle eating the rare slice of cake without it wreaking havoc on your metabolic health.
But if you continuously follow a high-carb diet, switching over to low-carb may cause headaches, cravings, and exhaustion. You don’t yet have the ability to be ‘flexible.’
We’ll talk more about how to fix this later on.
So, why bother with metabolic flexibility in the first place?
There are many reasons why you should pursue metabolic flexibility. Firstly, because it can dramatically increase your healthspan. But secondly, because it can help ward off chronic disease. Studies link metabolic inflexibility with conditions like obesity, diabetes, and heart disease.
So if you’re not metabolically flexible, now is an excellent time to reassess your lifestyle habits.
How can you tell if you’re metabolically flexible?
The most scientific way to know if you’re metabolically flexible is to complete an exercise test. One version of this is performed at the University of Colorado: patients jump on a bike or treadmill, wear a facemask, and provide regular fingertip blood samples for about 30 minutes. The test determines how well your body clears out lactate, which is a byproduct of your mitochondria when producing energy.
The next best thing is to order some bloodwork, then interpret your results according to healthy metabolic norms. For example, you may want to test breath ketones, hemoglobin A1c, fasting glucose and insulin, and your hs-CRP.
You can also take my free metabolic health quiz to determine whether or not you’re likely to be metabolically healthy.
If none of this sounds feasible, you can usually determine metabolic flexibility in other ways. One way is to reflect on the symptoms you experience in everyday life. For example:
- Low energy after eating, especially if it’s been two or three hours
- Trouble losing weight even though you’ve tried eating fewer calories
- Increased blood sugar levels, even if you haven’t been diagnosed with prediabetes
If any of these sound like a recurring problem to you, you’re likely struggling with an inflexible metabolism.
How does exercise impact metabolic flexibility?
The biological function of exercise and your metabolism boils down to one thing: energy.
You need energy to exercise. Your body must then produce multiple types of energy depending on your physical demands.
Let’s take a closer look at the biological function:
- When you exercise, your muscles burn through stored glucose (glycogen) for energy. But when you run out of glucose, you’ll need alternative fuel sources.
- Physical activity increases the number of glucose transporters (GLUT4) on muscle cell surfaces. This allows them to absorb glucose more efficiently without requiring as much insulin. They’re also better equipped to break down fatty acids and use them for fuel.
- Regular exercise trains your body to switch fuel sources efficiently. Each workout session reinforces the metabolic pathways needed to transition smoothly between burning carbs during activity and burning fat during rest.
Even a minimal amount of exercise creates lasting adaptations. Case in point: just one hour of moderate exercise per week can improve your metabolic flexibility. You might see changes to insulin sensitivity appearing within days, and improved metabolic health in as little as two weeks.
Let’s take a closer look at how to expedite this in your own routine.
3 ways to increase your metabolic flexibility with exercise
Now that we’ve talked about the nuts and bolts of metabolic flexibility, let’s spend a little more time exploring how to increase it.
Or, as Dr. Iñigo San Millán calls it, a discussion on “metabolic rehabilitation.”
1. Exercise while fasted
Exercising without much food-produced energy in your body forces it to rely on stored energy sources (such as the fat in your liver).
Now, you don’t need to fast for multiple days to see these effects. Even an eight-hour eating window can offer some benefits, such as doing a workout before breakfast.
You can learn more about how this works in my guide to building a fasting routine.
2. Resistance train rather than cardio-only exercise
You likely already know that resistance training increases muscle mass. But you should also know that muscle tissue is metabolically active, which means it requires more energy at rest than fat tissue. The more muscular you are, the more energy your body will burn, and the more likely you are to manage your energy stores consistently.
Strength training also enhances insulin sensitivity more effectively than cardio alone. That’s because when you lift weights, you create micro-tears in muscle fibers. This repair process demands energy and upregulates the proteins responsible for glucose uptake, which makes your muscles better at absorbing and storing glucose without excessive insulin.
No need to start with two-hour weight training sessions. Often, you can fit in resistance training within 30 minutes per day.
3. Switch between high-intensity and low-intensity workouts
Metabolic flexibility improves when you train your body to use different fuel sources in different contexts. Varying your workout intensity is one of the most effective ways to do this.
A 2025 study published in the Journal of Clinical Medicine directly compared short-term HIIT with moderate-intensity continuous training in adults with obesity. Both exercise types improved glucose tolerance, but HIIT appeared to have a more advantageous effect on metabolic flexibility.
Learn more about the best exercises for your cardiovascular health.
