What is Metabolic Flexibility?

Large portions of the human population are in a constant struggle when it comes to their metabolic health. While our bodies are naturally capable of adapting to a variety of food sources and quantities, how we take care of ourselves in our daily lives directly affects how efficiently we are able to process and store the food that we consume.

Metabolic flexibility (MetF) is defined by Dr. Zhang as, “the ability to rapidly switch between the use of carbohydrates and fats as sources for energy, based on nutrient availability.” When we are operating at a high rate of MetF, storage of fuel as well as efficient utilization of stored food are both accomplishable. This gives us complete control over our bodies from both aesthetic and overall health standpoints. Metabolic elasticity is critical to human survival during times of scarcity, but it also allows for the basic enjoyment of stimulation provided by the availability and/or abundance of food.

The human body primarily uses two sources for fuel: carbs and fats. We have the biological ability to be efficient at using both, much like a hybrid car that can switch between electricity and gasoline. However, when we consistently operate with an imbalanced diet, we stray away from our optimal capabilities. Due to an overconsumption of sugars, both complex and simple, many people have lost their metabolic flexibility and are stuck in a carbohydrate burning metabolic state. When this happens, sugar cravings intensify and kickstart a vicious cycle of blood sugar spikes and crashes that can have a major impact on our health. This often leads to unfavorable side effects that are precursors to modern diseases such as diabetes and autoimmune disorders. 

Fat Metabolism

Understanding fat metabolism is critical to your health. To begin, there are two types of fats we get from our food: saturated and unsaturated fats. The difference between saturated and unsaturated fat lies in the number of double bonds in the fatty acid chain. Saturated fatty acids lack double bonds between the individual carbon atoms, while unsaturated fatty acids have at least one double bond in the fatty acid chain. This structural difference determines the way in which your body uses and stores these fats. Saturated fats come from animals and fruits, and unsaturated fats come from vegetables, nuts, and seeds. Saturated fats are also solid at room temperature, while unsaturated fats are liquid.

Unsaturated Fats

Humans can process both saturated and unsaturated fats, but our ancestral history has led us to more efficiently utilize saturated fats. Unsaturated fats cause more fat growth and buildup, especially in the visceral (belly) region. While unsaturated fats, primarily linoleic acid, do play a role in human health, they are needed only in small amounts. This is consistent with evolution, as these fats were only available in limited quantities until the advent of farming. Industrial production of polyunsaturated oils such as soy, canola, sunflower, safflower, and corn oils have significantly increased the amount of polyunsaturated fats in the human diet. Industrial processing also introduces several types of toxins into these oils as byproducts of the heating process required for extraction. Linoleic acid content is also 10–20 times higher in produce from grain-fed in factory farming operations.

Saturated Fats

When we consume saturated fats, mitochondrial respiration sends signals to the fat cells (adipocytes) to resist storing these fats. Instead of storing these fats, the body has evolved to keep them available for more energy production. Animal fat, a little bit of butter, eggs, and coconut or avocado oil are great examples of reliable and delicious sources of saturated fats. These food sources are easily converted to ketones in the liver to provide our brains and muscles with energy. Saturated fats have even been linked to the prevention of metabolic syndrome in cases of excess carbohydrate consumption!

Insulin’s Role

Insulin plays a key role in modulating the type of calories we burn for our body’s energy. When we eat a meal loaded with carbohydrates, our insulin production increases. This Insulin then stimulates the use of glucose for energy and storage of both carbohydrates and fatty acids from the food we eat. When our food intake matches fuel expenditure, we will remain at the same bodyweight. Weight loss or weight gain can be accomplished by considering the simple mathematical equation made by taking into consideration both energy input and output. When caloric intake exceeds fuel needs, excess calories are stored as fat to be accessed at a future date when we need more calories for energy. Moreover, if caloric expenditure exceeds daily fuel intake, then stored fat will be burnt as necessary.

The Evolution of Metabolic Flexibility

Humans have evolved and adapted through a variety of circumstances over our long history here on Earth. We have experienced cycles of nature repeatedly, over and over again. The universal seasons have brought about times of abundance and feasting, as well as times of scarcity. Depending on the month or year, one’s eating habits are very likely to change. In fact, rarely do humans ever maintain the same eating habits for long periods of time. Psychologically, we are wired to seek the stimulation and endorphins provided via the consumption of different foods containing nutrients necessary for survival.

Food availability is also dependent on a wide spread of factors from person to person. For example, a small rural village with a successful harvest is able to fulfill its population with a greater caloric intake for the year to come. As our food systems have become modernized and manipulated for mass production, many people have strayed away from our evolved eating habits. With fast food, supermarkets and grocery stores easily accessible, all it takes is a trip in the car (and you can even have that done for you) to instantly obtain all of the food you can possibly want. Today we see a pattern of high-caloric, low-nutrient diets amongst many industrialized cultures.

Metabolic Inflexibility / Metabolic Syndrome

Metabolic inflexibility (MetIF) is linked to Metabolic Syndrome and to many chronic diseases. While it may seem obvious that overconsumption of calorie-dense food is the root cause, it turns out to be much more complicated. Poor sleep, high stress, environmental toxicants, and poor exercise habits can all throw off our circadian rhythms. To reinstate metabolic flexibility in metabolically ill people, all of these factors must be addressed.

Someone who has become metabolically inflexible cannot easily mobilize fat from storage into use as fuel for energy. Instead, they become dependent on frequent meal spacing to stay fueled with carbohydrates and keep their body pumping. It becomes increasingly difficult to eat exactly the number of calories needed for energy each day. This makes it nearly impossible to sustain a sub-caloric diet, achieving weight loss and re-establishing metabolic flexibility.

Making A Change

Making a metabolic correction isn’t always easy, but it is important to address all factors which might play a role. Cultural norms, personal preferences and work requirements are great examples of how individuals differ from one to the next. The next step is to introduce a nutrient-dense, minimally processed and low-pesticide diet. Proper fuel combined with sleep optimization and a manageable physical activity schedule will lead to optimal metabolic and overall health.

This metabolic shift will provide many important health benefits including:

• Increased energy, focus, and mental clarity

• Weight loss

• Improved insulin sensitivity and decreased blood glucose

• Increased stem cell production

• Improved hormonal balance

• Improved detoxification

• Changes in genetic expression (turning off bad genes and autoimmune diseases)

• Decreased inflammation and pain

• Decreased sugar and food cravings

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When you keto-adapt, your body becomes efficient at burning fat. That makes it easier to lose weight. Not only that, but you get a renewed sense of energy and confidence to finally engage in life in ways that matter to you. It empowers you to step into more of who you want to be.

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Sources

Zhang, S., Hulver, M.W., McMillan, R.P. et al. The pivotal role of pyruvate dehydrogenase kinases in metabolic flexibility. Nutr Metab (Lond) 11, 10 (2014).

Some information for this article was obtained from the “Metabolic Reset” program manual, created by Dr. Jim Bentz.

Metabolic Reset: Achieving Flexibility with Proper Nutrition and Daily Habits