Metabolic Flexibility: Function and Benefits

What is metabolic flexibility?

In simple terms, metabolic flexibility is our bodies ability to switch efficiently between different types of fuel - carbs or fat -  depending on what's available, and what’s needed at any given time.

It’s essentially like having a car that can run on both gas and electric. It gives you more options and makes you less reliant on one fuel source, improving our day-to-day performance and helping maintain our long-term health. 
So why does it really matter and how does this happen? Let’s get into this.

Why does metabolic flexibility even exist?

Metabolic flexibility was shaped over the course of millions years of evolution by our ancestors' nomadic lifestyle.

Humans evolved from lifestyles in which prolonged energy deficit was predominant to energy supply. Meaning, we didn’t eat far more frequently than we actually ate. Food was scarce and unpredictable, and daily living involved long periods of fasting and short periods of feeding.

In order to survive, our body had to become “flexible” and learn how to adapt quickly to different conditions. Humans had to store energy in the form of glycogen and body fat in anticipation of food shortages. And then quickly and efficiently access these storages when needed most. This was an evolutionary advantage that helped us survive.

Why do we need metabolic flexibility

Overall, metabolic flexibility is essential for maintaining day-to-day performance, promoting optimal organ function, managing weight, adapting to dietary changes, and reducing the risk of chronic diseases.

But what does this mean in simple terms? And how does it help with fasting?

1. We can trust our body to tell us when we are truly hungry/full

By regulating hormones like insulin, ghrelin, leptin, and peptide YY, metabolic flexibility ensures the accuracy of our body's hunger and satiety signals. This enables us to trust our body's cues and know when we genuinely need to eat, in the right quantities, and with the appropriate food choices. Metabolic flexibility empowers us to maintain a balanced and intuitive approach to eating, ensuring that we nourish ourselves precisely as required by our body's needs.

2. We become better at controlling hunger

Hunger is a natural response to fasting, but not all hunger signals require immediate action. Individuals with metabolic flexibility excel at regulating blood sugar levels and are less reliant on constant food intake for energy. They can efficiently switch to utilizing stored fuel sources, resulting in more manageable hunger signals and reduced cravings during fasting periods.

3. We don’t “crash” during our fasting window

Because our body is better at responding to nutrient availability than waiting for the next meal, it quickly breaks down fat storage to make sure we feel and perform well even without food. It's like having a built-in backup battery that provides a steady stream of energy to help us carry out our day-to-day tasks effectively.

4. We can burn more body fat / preserve muscle better

By effectively utilizing stored fat for energy, metabolic flexibility promotes fat burning, while preserving muscle mass by prioritizing its preservation over being used as an energy source. This helps us achieve a healthier body composition with reduced body fat and preserved lean muscle mass.

5. We can “eat what we want” (in moderation of course)

Probably the most valuable benefit of all, the more metabolically flexible we are, the less we have to micromanage our macronutrients and calories. We are less likely to gain weight and feel great after we have fries or a slice of cake. 

6. We’re better at managing our long-term health

By efficiently switching between fuel sources, metabolic flexibility optimizes mitochondrial function, leading to enhanced energy production, improved cellular health, and reduced oxidative stress. This improved mitochondrial function supports overall longevity, health span, and resilience against age-related diseases.

What causes metabolic inflexibility

In the last few hundred years our environment has drastically changed. We now have continuous access to high-caloric low-nutrient foods, we exercise less and stress more, and use medications that disrupt bodily functions. There’s a big mismatch between our metabolic evolution and our modern environment that triggers issues with our mitochondria - the power plants of the cells that are responsible for turning food into usable energy.

The fewer mitochondria cells someone has, and the more dysfunctional they are, the less flexible and more compromised their energy production is.
When you have too little and poorly functioning mitochondria it makes it hard for the body to produce as much energy.  When there's already a lot of energy floating around inside the cells, they don't want more of it. So, instead of letting insulin do its job and bring in more energy, the cells become less sensitive to insulin. It's like the cells are saying, "We don't need any more energy right now!" 

This is called insulin resistance, and it's where the trouble starts. This can lead to high levels of sugar in our blood and cause problems like weight gain, high blood pressure, and diabetes.

It also makes switching between energy sources very difficult. When we can’t use stored fat for energy between meals, snacking (or frequent eating) is inevitable. And when we don’t burn the fuel we eat, we’re contributing to energy access.

This is where trouble begins because it sets the stage for insulin resistance and type 2 diabetes.

Signs of poor metabolic flexibility:
  • You have strong cravings and unstable appetite 
  • You need to snack to get energy going
  • Going 5 hours without a meal and fasting in general are very difficult
  • You’re not losing body fat when fasting
  • You “crash” after each meal

How to regain metabolic flexibility

To regain metabolic flexibility we simply need to force the body under conditions where it has no choice but to start burning fast for energy.  

  •  Exercise: 

Engage in a combination of cardiovascular exercises and strength training to improve insulin sensitivity and help restore ability to burn fat. Higher demand for energy will condition the body to break down body fat, as well as promote creation of new mitochondria. Aim for at least 150 minutes of moderate-intensity aerobic activity per week, along with resistance training two or more days a week. Fasted workouts are welcomed.

  • Get fat-adapted

Try limiting the amount of carbs you supply to your body on a daily basis. We can only hold up to 400 gr of stored glucose (glycogen) in the body, and limiting (lowering) carb intake can help reduce reliance on glucose as the primary fuel source and encourage the body to utilize alternative energy pathways. 
Then, after a few weeks, tailor your carbs intake based on your activity level.

  • Do Intermittent Fasting or Time-Restricted Eating

Incorporate periods of fasting or time-restricted eating into your routine. Prolonged periods without food will teach the body to use stored energy between meals and help regulate hunger hormones, improve appetite control, and support overall metabolic health. Start with conservative fasting windows and gradually increase duration based on personal comfort and tolerance.

  • Ensure your body has the right nutrients

Start consuming a balanced diet that provides a variety of micronutrients that play a crucial role in regaining metabolic flexibility. Adequate levels of vitamins and minerals support various metabolic processes, including energy production, hormone regulation, and cellular function. For example, nutrients like magnesium, zinc, and vitamin D are involved in insulin sensitivity and glucose metabolism.

Conclusion

Regaining metabolic flexibility might seem like a challenging task at first. However, this should be a focus of anyone who strives to optimize their body's energy utilization and pave the way for better long-term health. The best way to approach it is to create sustainable practices by integrating small, manageable habits into our daily lives. Start by incorporating regular exercise, making healthier food choices, gradually implementing fasting or time-restricted eating, and prioritizing self-care and stress management. Remember that progress takes time, and consistency is key. By embracing these lifestyle changes and committing to the journey of improving metabolic flexibility, we can unlock the potential for a healthier, more balanced life.