Metabolic flexibility. What is it?

The ability of the human body to burn the more readily available fuels in our diets. Basically, our body can burn either carbs or fat for energy. Metabolic flexibility is your bodies ability to easily switch back and forth between the two fuel sources.


This is mostly done through insulin. If you have higher insulin levels your preferred source of fuel will be carbs. Lower insulin, you will burn fat better as a fuel source.


Metabolic flexibility is caused by a few different factors.

  • Genetics. People with a family history of diabetes will usually have a tougher time burning carbs as fuel. Insulin shuts down your ability to burn fat as fuel.



  • Inactivity. Excess fat stored in the body causes only problems. Proper diet and exercise will mitigate this in most people.




  • Decreased mitochondrial function. When mitochondria are not functioning correctly your body will have trouble with proper fuel selection. Lifestyle factors such as oxidative stress, toxicity, and inflammation directly contribute to your metabolic inflexibility.




  • Insulin Resistance. Basically, insulin resistance is your body not listening to the insulin that is released when you eat, the insulin wants to lower your blood sugar but your body won’t cooperate. Over time your body creates more and more insulin when you consume carbs just to keep blood glucose levels from skyrocketing.



When you rely on low-quality carbs(processed, or sugar-laden) for long periods of time you develop insulin resistance. This means you won’t make energy properly no matter what you are eating.


How do we increase our metabolic flexibility?

  • Exercise. As usual, exercise will help fix your metabolic inflexibility. Exercise especially strength exercise will help hormonal balance which in turn helps rebuild mitochondrial function.
  • Lower sugar intake. Especially in the mornings. Starting your day without an insulin dump will help you regain your metabolic flexibility faster. Think higher fat, moderate protein, and light carbohydrate breakfast. For example 2-4 eggs, ½ an avocado, some lightly sauteed greens and some berries on the side.
  • Reduce carbohydrate intake. You don’t need to cut out carbs but instead, reduce carb intake. If you are metabolically inflexible, you have trouble burning body fat for fuel. Restricting your carb intake forces your body to rely on fat as a fuel source. Don’t cut carbs out, just reduce them. Start by eliminating sugar, calorically rich beverages, and refined grains.
  • Eating a high fiber diet. High fiber diets are highly anti-inflammatory. Fiber slows the release of insulin into the bloodstream and signals the liver to produce less glucose. Fiber has other benefits that are directly associated with a healthy lifestyle and lowering body fat levels. Fiber keeps you full longer, so you don’t reach for snacks in between meals. Consuming adequate fiber also helps improve the absorption of nutrients in the gut. Get your fiber in people!
  • Stop eating 6 times a day. This is dietary dogma at it’s finest. There is no such thing as stoking your metabolism. Eating less frequently has been shown to improve almost every single avenue of fat loss and overall health. You need to be able to give your body time to burn the fuel you have put inside it. If you are eating every 2-3 hours you are never tapping into your internal energy stores(body fat). This is vital to develop your metabolic flexibility.


How do you figure out how metabolically flexible you are?








1. Have a high carb meal first thing in the morning on an empty stomach. If you feel like crashing and taking a nap shortly after eating the said meal you may have high insulin and probably don’t burn carbs well.

2. Fast. If you get hungry after 2 hours without food you have low insulin levels and cannot burn body fat for fuel. If you are metabolically flexible you should be able to go 5-6 hr without food because your body will tap into body fat stores for fuel.


This is the simplest way to figure out how insulin sensitive you are.


A more accurate way would be with a blood glucose monitor. Where you prick your finger and take readings when you have fasted, and shortly after eating different meals/foods. It’s not just carbs that can cause an insulin response either. Having too much protein at one time can also cause an insulin spike in some people.


One of the perks of being very metabolically flexible is that you can enjoy some not so optimal foods once in a while and not worry about anything because your body is good at burning either fuel source for energy.

If it were only that simple……

A big key to look at is individualized metabolic flexibility. It’s not just low-quality carbs that cause insulin spikes. There has been a ton of documented research showing that some people can eat a chocolate chip cookie and get a limited insulin response but if they eat a sweet potato their insulin goes through the roof.


What does this mean?

We are all incredibly different and you need to figure out what foods cause an insulin response for you and which don’t. That’s the tough part about nutrition is that we are all so different. Telling people to just eat real food all the time and never have unhealthy treats is unrealistic and unnecessary. Just because you enjoy yourself once in a while with a moderate amount of sugar doesn’t mean you are all the sudden going to get sick and die.


Insulin resistance is closely connected to metabolic inflexibility because it increases your reliance on sugar for fuel. Which means your body fat stays where it is. On your body.


I used to love to use the term moderation but I have found that most people really have trouble with what moderation really is. The thing is, is that moderation for me is different then moderation for you.


Notice a trend here? WE ARE ALL DIFFERENT.


What works for me probably won’t work for you. What worked for Sally down the street isn’t going to work for your grandmother and so on.


Back in the day when we had to fight/hunt/forage for every scrap of food we had we were incredibly metabolically flexible. We never knew what kind of fuel source we were going to get that day. 


We need a wide variety of proteins, a plethora of different colored fruits, vegetables, a good amount of healthy fats and some carbs. I say some carbs because people who need to lose a lot of body fat do not need to eat that many carbs. They need to build the metabolic flexibility by spacing out their meals to around every 4 hours. Having balanced meals spaced out through your day will help you build that metabolic flexibility we all need to optimize our health.


The bottom line is we must be able to be flexible with our diets. Not so we can enjoy unhealthy food more often but more importantly to support our busy lives. Some days it is probably easy for you to meal prep and get all of your needed calories. Some days it will be very hard. These are the days when metabolic flexibility will save you.


When you are metabolically flexible you can easily go 6 or more hours without eating because your body can tap into fat stores for fuel. Even more so metabolic flexibility will help you not feel starving every 2 hours so you can be more productive and get more work done so you have more time for family and friends.


General Recommendations for metabolic flexibility


If your goals are to increase performance:

  • Use fat as your primary fuel source. The amount of food you take indirectly affects what your body uses as a fuel source.
  • Keep your insulin levels low to moderate during the day.
  • Get your insulin levels up prior to training or whatever it is you are trying to improve your performance in. (sports, CrossFit, etc).


If you have a hard time using carbs as a fuel source:

  • Try having a small portion of carbs in the morning.
  • Have some intra/post workout carbs, around halfway through the workout or post workout. This is when your body is looking to use glucose as fuel. So feed it.


To really drive performance you need to find the balance of optimal calorie intake. How much food can you eat where it improves your performance and you don’t gain any fat.

How can you tell if you are becoming metabolically flexible?


  1. Performance- Your performance in the gym and your daily energy levels should improve.
  2. Mirror- Your body should look leaner, especially in the abdominal region.
  3. Scale- Lastly and least important, because there are so many factors involved in how much you weigh, the scale should be going down.

That is metabolic flexibility in a nutshell. This is a complicated process in our bodies and it will not be the same for everyone. This is a huge reason why nutrition should be individual. ALWAYS. There is no cookie cutter for your individual nutritional needs.


If you feel you need to be more metabolically flexible and want some help. I would love to walk you through setting up your diet to optimize your metabolism. Drop me a line here, and I can help you out with making some changes.