metabolic flexibility

What’s Metabolic Flexibility and How to Achieve It?

Our body has a default system to produce and use energy, but what if we could change that to make it more efficient? Metabolic flexibility permits to use different fuels for energy, making energy production much more effective. Now the question is; What is it and How I can achieve it?

In this post, we'll talk about metabolic flexibility and different strategies to follow and achieve it. Easy applications you can implement on your lifestyle to be better at producing energy and feeling adapted to different stressful situations.

What’s Metabolic Flexibility

The concept of Metabolic Flexibility refers to 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 if a car could use both diesel and gasoline.

As default, our metabolism will use carbohydrates and blood glucose to produce energy. When glucose is absent, glyconeogenesis is activated to produce more glucose from glycogen stores. As we run out of glycogen and no more glucose is present in the bloodstream, we activate lipolysis and fat oxidation to produce energy from fatty acids stored in adipocytes (read more about Fat Oxidation HERE)


Do we Have Metabolic Flexibility?

The diagram above shows the traditional and popular flow of energy production. However, science has shown that this is not quite true (study). We, humans, have developed the ability of producing energy from different fuels, such as carbohydrates, fats, or even amino acids. Therefore, sorry to disappoint you, but everyone has metabolic flexibility from a start point.

Modern society, abundant in high glycemic carbohydrates and refined sugars, has tremendously raised glucose in our diet. If we keep the same nutritional habits over time (which we do), we adapt to using carbohydrates as the sole energy source, and fat is not further needed for energy production.

Our lifestyle is what determines our metabolic flexibility. From an evolutionary perspective, we do have metabolic flexibility. But if we start eating a lot of carbohdyrates for no reason, bad eating-behaviour, sedentarism, metabolic diseases,... we'll lose metabolic flexibility over time (study)

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 What Leads to Metabolic Inflexibility?

Now you know that, as humans, we do have metabolic flexibility. But most of us lose it. Why? Although it's a multifactorial event, we'll cover the main causes here.

Western Diet

If you look at the composition of a normal western diet, you can note the abundance of refined sugars, flours, and hugh glycemic carbohydrates (source). Driving the obesity pandemics (study), Western Diet is also one of the main cause of our metabolic inflexibility (study).


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, opposite to insulin sensitivity, happens when our 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), it is also one of the main causes of metabolic inflexibility, maintaining high blood glucose levels for long periods of time.

How Can We Achieve Metabolic Flexibility?

Although we naturally have metabolic flexibility, environmental factors can modulate our metablism and disturb it. But don't worry. If this is your case, there are some protocols you can use to go back on track and achieve metabolic flexibility.

how to achieve 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). Not only that, but 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, our metabolism will adapt to fats being the main source of energy during fasting. This will improve your metabolic flexibility. And to make it even better, a high-fat intermittent fasting protocol could enhance those benefits (study).

With some considerable evidence backing up this protocol, we can conclude that 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.

Intermittent fasting and metabolic flexibility

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, in where glucose is oxidized to induce the electron transport chain and produce energy (study).

When all glucose available is oxidized, triglycerides are released into the extracellular medium from adipocytes and used for energy production (study)

Fat Metabolism during Exercise

Increased fat oxidation during exercise has been associated with a higher metabolic flexibility (study). The ability to use fatty acids to produce energy as well makes us better at shifting between carbohydrates and fats as fuels for energy production.

In fact, fats are more energetically dense than carbohydrates and proteins (study). This is, the same amount of fats will yield higher amounts of energy than if carbohydrates were used. Therefore, if we are able to use fats more often for energy production, it could improve our exercise energy metabolism

Minimize Refined Carbohydrates

Refined carbohydrates, abundant in the Western Diets, are non-satiating and non-nutritious dietary options. Associated with obesity and weight gain, refined carbohydrates increase glycemic index and blood glucose levels (study).

If we have more glucose available for energy production, our metabolic flexibility will get worse and worse. 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, the absence of glucose leads to using fats to produce energy and form ketone bodies, also used for energy production (source).

One of the main advantages of doing a ketogenic diet is the improved glucose metabolism. Ketogenic diet has shown to decrease HOMA-IR (marker of insulin resistance) and improve weight loss (study). Following this diet, we'll be able to use fats and ketone bodies for energy production, but carbohydrates will be absent.

This is not what we want at all. When we talk about metabolic flexibility, we want to take advantage of all substrates to produce energy, and shift between them. While ketogenic diet may not be the best option to achieve that, a flexible ketogenic diet may be the key.

flexible ketogenic diet

In this protocol, ketosis is induced periodically, let's say every three months (12 weeks). After those 12 weeks, it's time to induce a short-term ketosis, of about one month (4 weeks).

What we are interested on here is to lower plasma glucose concentrations and higher fat oxidation, specially during exercise. Four weeks have shown to be enough to achieve these, but you can extend it for longer if you want (study)

Practice Resistance Training

Resistance training and anaerobic exercise are sport disciplines widely known for their benefits on our health and metabolism (read more). In today's field of interest, resistance training can improve glucose homeostasis (study). By increasing insulin secretion, resistance training is able to improve glucose uptake and lower blood glucose (study).

Resistance training also increases fat oxidation and utilization for energy production (study). Overall, what resistance training does is to speed up our metabolim and 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). Because of their body composition, obese subjects show an increased energy production from carbohydrates, but considerably lower from fats (study).

In presence of carbohydrates, these will be the preferred substrate for energy production. 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.

Obesity and metabolic flexibility

The release of fatty acids and extraction of triglycerides was considerable lower in obese than lean males(source). Obese subjects were worse at moving fatty acids through the plasma, which translates to a worse energy metabolism.

To avoid metabolic inflexibility, lower your body weight and improve body composition. Start by doing physical exercise, preferrably resistance training (read more), and follow a nutritional plan to induce weight loss (read more).


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.

We naturally have metabolic flexibility, but modern society and lifestyle are the main cause of metabolic inflexibility. In this post, however, we saw how to solve this and achieve metabolic flexibility.

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