Your body has a default system to produce and use energy, but what if you could change it to make it more efficient?
Metabolic flexibility permits to use different fuels for energy, making energy production much more effective.
In this post, we'll talk about metabolic flexibility and different strategies to follow and achieve it.
What’s Metabolic Flexibility?
Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand (source).
In other words, it's the ability of using different fuels to produce energy (like a hybrid car)
As default, your metabolism will use glucose to produce energy. When glucose is absent, your body makes more glucose from glycogen stores.
When glycogen storages are empty, your body will produce energy from fatty acids stored in adipocytes.
Do You Have Metabolic Flexibility?
The diagram shows the traditional flow of energy in your body... although it may not be entirely true(study).
You, humans, have developed the ability to produce energy from different fuels, such as carbohydrates, fats, or even amino acids.
Therefore, everyone has metabolic flexibility from a start point.
Your lifestyle is what determines your metabolic flexibility. From an evolutionary perspective, you do have metabolic flexibility.
But eating a lot of carbohdyrates for no reason, bad eating-behaviour, sedentarism, metabolic diseases,... will make you lose metabolic flexibility over time (study)
 What Leads to Metabolic Inflexibility?
Now you know that, as humans, we do have metabolic flexibility. But most of us lose it.
What are the cause of metabolic inflexibility?
Western Diet
Western diets are abundant in refined sugars, flours, and high glycemic carbohydrates (source).
Driving the obesity pandemics (study), Western Diet is also one of the main cause of our metabolic inflexibility (study).
Sedentarism
Physical exercise enhances fat oxidation and improves insulin sensitivity (study). Insulin sensitivity will help you lowering blood glucose faster, thus being able to use fat for energy production as well.
Insulin Resistance
Insulin resistance happens when your pancreas is deffective at producing insulin, or insulin itself is not as effective at doing its job, therefore needing more insulin to do the same task (study).
Being the cause of a lot of metabolic diseases (study), insulin resistance is also one of the main causes of metabolic inflexibility, maintaining high blood glucose levels for long periods of time.
How Can You Achieve Metabolic Flexibility?
Although you naturally have metabolic flexibility, environmental factors can modulate your metablism and disturb it.
If this is your case, there are some protocols you can use to go back on track and achieve the desired metabolic flexibility.
Intermittent Fasting
Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting.
It reduces blood pressure, inflammatory markers and blood lipid profile (study). It also improves insulin sensitivity and glycemic control (study).
Because of the restricted timing, it can also help losing weight while "enjoying" more food during the eating periods.
There are many protocols of intermittent fasting (study). To make it easy and adhering, the protocol 16/8 seems to be the best option (16h fasting - 8h eating).
During the fasting periods, blood glucose levels are low. To produce energy, your metabolism to fats as main source of energy.
This will improve your metabolic flexibility. A high-fat intermittent fasting protocol could enhance those benefits (study).
Intermittent fasting could be a useful strategy to work on our metabolic flexibility. It helps losing weight, improving insulin sensitivity and glycemic control, and using more triglycerides as energy source.
Aerobic Exercise
Aerobic exercise involves the use of oxygen for energy production. On the presence of oxygen, the primary exercise energy system is the oxidative pathway.
Glucose is oxidized to induce the electron transport chain and produce energy (study).
When all glucose available is oxidized, triglycerides used for energy production (study)
An increase in fat oxidation during exercise increases your metabolic flexibility (study).
The ability to use fatty acids to produce energy makes you better at shifting between carbohydrates and fats as fuels for energy production.
If you are able to use fats more often for energy production, it could improve our exercise energy metabolism
Minimize Refined Carbohydrates
Refined carbohydrates are non-satiating and low-nutritious dietary options.
Associated with obesity and weight gain, refined carbohydrates increase glycemic index and blood glucose levels (study).
The more glucose available during prolonged times, the less fat will be used as energy source (study)
If you want to have metabolic flexibility, you'll need to regulate and reduce refined sugars in your diet.
Base your nutrition in whole low-moderate glycemic load foods, and avoid ultraprocessed foods and high glycemic load options.
Flexible Ketogenic Diet
Ketogenic Diet is a nutritional strategy consisting of high fat, adequate protein and low carbohydrate intake (source).
During ketosis, your body uses fats to produce ketone bodies to replace glucose as main energy source(source).
Ketogenic diet decreases HOMA-IR, a marker of insulin resistance, and improves weight loss (study).
Following this diet, you'll be able to use fats and ketone bodies for energy production, but carbohydrates will be absent.
A flexible ketogenic diet can help you train your body to use different substrates to produce energy (study).
In this protocol, ketosis is induced periodically for 12 weeks. After those 12 weeks, it is time to induce a short-term ketosis of about one month (4 weeks).
Practice Resistance Training
Resistance training and anaerobic exercise are widely known for their benefits on your health and metabolism.
Resistance training can improve glucose homeostasis (study). By increasing insulin secretion, it is able to improve glucose uptake and lower blood glucose (study).
Resistance training also increases fat oxidation and utilization for energy production (study).
It speeds up your metabolim to make it more efficient at using different substrates for energy production. Thus, resistance training is a recommended practice to achieve metabolic flexibility.
Improve Body Composition
Fat percentage, body mass index and weight are associated with metabolic inflexibility (study). Obese subjects show an increased energy production from carbohydrates, but considerably lower from fats (study).
In obese subjects, glucose is available most of the time, and the usual lower energy expenditure and lifestyle of these subjects don't demand of more energy than the provided by carbohydrates.
The release of fatty acids and extraction of triglycerides was considerable lower in obese than lean males(source).
To avoid metabolic inflexibility, lower your body weight and improve body composition. Do physical exercise and follow a weight loss diet plan.
Conclusion
Metabolic flexibility is the ability to respond and adat to conditional changes in metabolic demands.
By using different fuels, one can improve energy metabolism and consequently improve sports performance and calorie expenditure.
You naturally have metabolic flexibility, but modern society and lifestyle are the main cause of metabolic inflexibility.
