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Nutrition

Get excited about nutrition, and learn as you go with these information-packed resources on a wide variety of nutrition-centric topics! Our bistroMD experts review the importance of the macronutrients protein, fat, and carbohydrates, as well as how to make them work most efficiently for you.

What Is Metabolic Flexibility? Definition, Signs & More

Flexibility means being capable of bending easily without breaking so how might this concept impact metabolism? Learn the details about metabolic flexibility for true health here!

What Is Metabolic Flexibility? Definition, Signs & More


Being physically, emotionally, and mentally flexible offers tremendous benefits in the grand scheme of life. It not only eases stress but also makes it more manageable. 

So, what about metabolic flexibility? Is it just as important?

Health experts think so! Discover how to create metabolic flexibility to support health and wellbeing.

What Is Metabolic Flexibility?

The body's preferential form of fuel is carbohydrate. Carbs are quickly digested and can therefore be converted into ATP as cells need. However, metabolic flexibility refers to the ability to use whatever form of fuel is available.

Before readily available food at grocery stores, gas stations, sidewalk kiosks, and more, humans were innately metabolically flexible. On some days, food was readily available and at other times, hunters and foragers might have to make do without food for days at a time. In essence, their bodies would burn carbohydrates when available but could also tap into fat stores when necessary.

Today, metabolic flexibility can also be defined by the capacity to match fuel oxidation to fuel availability. If someone is very metabolically flexible, they will easily burn carbs when eaten rather than store them as fat, but will also burn fat after consumption or when fasting. 

It may seem like everyone is metabolically flexible, then, but this is certainly not the case. In fact, nearly one-third of adults in the US have metabolic syndrome, a myriad of five conditions including: 

• High blood pressure
• Elevated blood sugar and triglycerides
• Abnormal cholesterol
• Abdominal obesity

Furthermore, metabolic syndrome is synonymous with metabolic inflexibility. Some consequences of impaired metabolic flexibility include:

Insulin resistance
• Decreased mitochondrial function
• High fasting blood glucose levels
• Frequently feeling "hangry"
• Feeling sleepy after meals
• Mid-morning and afternoon energy crashes
• Increased abdominal obesity
• Needing to constantly snack
• Decreased exercise performance
• Increased feelings of depression, anxiety, irritability, and distraction
• Relying on carbohydrates for fuel

Metabolic inflexibility is largely a result of that first listed symptom - insulin resistance. Because insulin is an anabolic hormone, chronically elevated blood levels prevent the body from burning fat. It basically keeps the body in a building or storage phase. 

And all the while, glucose cannpt adequately get into cells. This causes strong carb cravings and all other symptoms of the blood sugar roller coaster.

Benefits of Metabolic Flexibility

On the other hand, metabolic flexibility offers many health benefits such as:

• Easy weight maintenance
• Easier ability to lose weight
• Improved mitochondrial function
• Increased energy levels
• Lower risk of developing metabolic syndrome/diseases
• Good blood glucose management
• Improved sleep patterns
• Optimized workout performance
• Improved mood 

Perhaps the greatest benefit of metabolic flexibility is a decreased need to micromanage food intake. The body trusts that it will usually receive the proper balance of nutrients, thus it digests, absorbs, and stores what is needed and uses the rest. 

Metabolically flexible individuals do not need to meticulously count calories or even macros to achieve health goals. Their bodies are flexible, adaptable, and efficient. Energy levels reflect fuel stores appropriately and hunger and fullness cues reset after heavy meals, naturally adjusting based on glucose levels and fat stores.

How to Become Metabolically Flexible

Becoming metabolically flexible largely means improving insulin sensitivity, and here are ways to do just that.

Exercise

Even though you cannot completely out-exercise a bad diet, physical activity inevitably improves insulin sensitivity. The chemical reactions that occur during exercise make cells more sensitive to insulin. 

Additionally, certain types of training like HIIT and long endurance aerobic training increase mitochondrial biogenesis (creation of new mitochondria). More mitochondria increases the ability to turn food into usable fuel.

Become Fat Adapted

This is the number one reason keto is one of the hottest eating plans amongst health communities right now. The keto diet, or a very high fat-diet, forces the body to use ketones as fuel and it induces metabolic shifts that cause the body to burn dietary and stored body fat for energy. Once in ketosis for a while, the body can easily shift between burning carbs if available or burning ketones.

However, going full keto is often unnecessary. Instead, one can practice cyclical keto, where one eats a low-carb diet, or about 100 grams of carbs, one day a week. This allows someone to maintain the ability to digest carbs properly and provides the body with a vital nutrient for many processes.

Eat Mostly Whole Foods

Whole foods are composed of food constituents like antioxidants, fiber, and other polyphenols that naturally promote blood glucose regulation and insulin sensitivity. With adequate moderation, eating a whole foods-based diet is typically low carb anyways. 

Plus, eating whole foods is the single best way to maintain proper cellular function in general.

Practice Intermittent Fasting

Intermittent fasting is another way to quickly adapt the body to burn fat for fuel. The eating technique teaches the body to tap into fat stores when glucose is not readily available and readily promotes cellular detoxification. This allows cells to turn over and regenerate even better.

Include Targeted Nutrients

Certain nutrients are vital for the ability to burn fat as fuel. For one, magnesium increases mitochondrial function and insulin sensitivity. Polyphenols in colorful plants and dark chocolate benefit metabolic flexibility. Omega-3 fatty acids found in oily fish decrease pro-inflammatory omega-6 fatty acids and also improve mitochondrial function. 

Overall, though, maintaining proper stores of all nutrients is important as well.

Signs of Metabolic Flexibility

Most people can internally feel whether they are metabolically flexible based on the absence of symptoms associated with metabolic inflexibility. Common indicative signs of metabolic flexibility include:

• Awaking in a state of mild ketosis most mornings
• Easily maintain a healthy weight
• Good fasting blood glucose levels
• Good fed-state blood glucose levels
• Lack of blood sugar spikes and crashes
• Not needing to sleep after eating carbs
• Sustainable energy levels throughout the day
• Feeling good during exercise
• Feeling motivated to do physical activity
• Generally displaying a good mood
• Ability to effectively deal with stress
• Being able to easily eat fewer than 50 grams of carb per day
• Being able to fast for a long period of time when needed (12+ hours)

Recapping Metabolic Flexibility

Achieving metabolic flexibility can be vital for health and longevity. It ensures that the body can switch and adapt to whatever fuel source is available with few consequences if any. 

In addition, improving metabolic flexibility allows one to eat freely without much micromanagement or worry of derailing health and wellness goals. It also generally prevents metabolic syndrome and other health conditions. 

Improving insulin sensitivity is the quickest way to achieve a flexible metabolism. Exercise, eating a whole foods diet, and intermittent fasting can greatly help as well. 

References:

Metabolic Flexibility: Everything You Need to Know to Get Started. RSS. Published March 24, 2021. www.nutrisense.io/blog/metabolic-flexibility

Sisson M. The Definitive Guide to Metabolic Flexibility. Mark's Daily Apple. September 17, 2019. www.marksdailyapple.com/definitive-guide-to-metabolic-flexibility/

Sperlazza C. What Is Metabolic Flexibility and How Can You Achieve It? Bulletproof. Published July 9, 2021. www.bulletproof.com/diet/weight-loss/metabolic-flexibility/.

Sydney Lappe's Photo
Written By Sydney Lappe, MS, RDN. Published on May 05, 2022. Updated on May 11, 2022.

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