Did you know that the concept of metabolic flexibility started with a worm? A parasitic one: the helminths. The term was first used in 1985 by Dr. Kohler to describe the ability of helminths to use either aerobic or anaerobic respiration to produce energy and metabolites depending on the environment.
The concept relates to the selection of fuel to keep the body alive: fat or sugar. A healthy individual will switch its energy sources depending on the context: physical activity, nocturnal or intermittent fasting, change of diet.
In this article, we will go through the importance of metabolic flexibility, why it matters? What are the consequences of metabolic inflexibility? And how to measure what the primary source of energy of your body is?
What is metabolic flexibility?
Our body is hard-wired for being metabolically flexible. For our ancient ancestors, switching from our fuel source to another was a matter of survival. They had to benefit from various types of food and switch to fat or glucose-burning mode in case of food scarcity. Obesity was not an issue then.
Nowadays, the abundance of food leads to metabolic diseases, diabetes, insulin resistance, hypertension, cardiovascular disease, high cholesterol with all the underlying health risks such as strokes or heart attacks. The so-called American made of fast food, snacks, and soda will bring thousands of calories to the body. When combined with a sedentary lifestyle, all of this extra energy is stored as fat that will end up most around our waist. Being fit is not as easy as it was just 50 years ago. It requires patience, commitment, and strict disciple, but the health benefits are enormous.
Using various energy sources while exercising is a simple example and will help us understand the concepts underlying how our organism will react to the increased needs for fuel while jogging or working out.
While exercising, the skeletal muscle pool can induce up to a 25 fold increase in energy demands. All of the energy sources within the body will be required to fulfill the spike in demand: Intramuscular glycogen, triglycerides, plasma glucose, and plasma fatty acid (mainly coming from abdominal subcutaneous fat lipolysis).
Athletes have tremendous metabolic flexibility that allows them to switch from our energy source to another quickly, but we are not all triathletes.
An increase in the mitochondria biogenesis while exercising will lead to anabolic flexibility leading to weight loss, especially in visceral fat, which is considered the main fat reserve.
Interestingly, liposuction or any other surgical removal of fatty tissue from the body will not improve fatty acid oxidation and metabolic health. Hence improving metabolic flexibility doesn’t come easily.
The conclusion is that there is no shortcut to improve your waistline and increase metabolic flexibility. Exercising is key. After all, “sweat is fat tears”, and the more you exercise, the better the body will gain the ability to switch to various energy sources.
How to measure metabolic flexibility?
Various methods have been suggested to measure metabolic flexibility. The analyses are usually performed in laboratories by:
- Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise (San-Millán & Brooks, 2017),
- Change in respiratory quotient (RQ) from the fasted state to the insulin-stimulated state
- Room Calorimetry (Leger, 2015)
All of these scientifically relevant methods are complex and involve going to the hospitals or to a lab.
Nowadays, new devices such as the Lumen offer the possibility of quickly and conveniently measuring the body’s energy source and assessing the evolution of metabolic flexibility.
Lumen is a small handheld device that analyzes the carbon dioxide levels in the exhaled breath to define whether the body uses fat or glucose as its primary energy source.
Lumen is now offered on a subscription basis at an affordable price. In addition, it comes with a very exhaustive companion app. available for iOS and Android that will help define the best-suited regimen to lose weight, maintain energy levels, and improve metabolic flexibility.
Check our full review of the Lumen to know more about the benefits of this small device that may well change the way you eat, exercise, and keep your metabolism health at optimal levels.
What are the benefits of metabolic flexibility?
Increased metabolic flexibility proved beneficial for:
- improve weight loss and weight management,
- building lean mass,
- develop a more robust immune system,
- more stable blood sugar levels,
- Prevent the development of metabolic diseases and syndromes,
- Improve sleep,
- Feel more energized with fewer cravings.
What happens when metabolic flexibility is impaired?
Insulin is the primary hormone involved in the regulation of blood sugar in the body. Insulin will instruct the different components of the body (liver, muscle) to store glucose for later use. The excess being transformed at fat leading to weight gain with all of the potential health risks linked to obesity and physical inactivity.
Insulin resistance is critical for the development of metabolic inflexibility.
Metabolic inflexibility can lead to numerous pathologies, including obesity. Excess calories are stored as triglycerides in peripheral fat that can lead to metabolic and cardiovascular diseases. Obesity will also lead to a state of chronic low-grade inflammatory syndromes.
Excessive body fat associated with insufficient exercise will be the two pillars that sustain insulin resistance and type II diabetes.
Metabolic inflexibility is also associated with increased risks of cancer. Conversely, recent clinical studies showed a reduction in cancer occurrence in populations submitted to caloric restriction.
With so much evidence pointing towards the health benefits of metabolic flexibility, the obvious question is how to improve it.
How do you achieve metabolic flexibility?
Achieving improved metabolic flexibility can be achieved either by exercising or by changing the diet. A combination of both being of course the best path to follow.
Ketogenic Diet
The ketogenic diet gained a lot of popularity in recent years. The underlying concept is to dramatically limit the consumption of carbohydrates to reach a state of Ketosis and use ketone bodies produced from fatty acid as the primary source of fuel.
This diet may imbalance the body’s consumption of proteins and lead to low blood pressure, kidney stones, and constipation. If, theoretically, the ketogenic diet could be considered as a way to increase metabolic flexibility, the potential side-effects need to be considered.
On top of that, even when the body is in a state of KetosisKetosis, glucose will still be used as gluconeogenesis will still convert part of the proteins into glucose.
Intermittent Fasting
According to a study conducted in 2018 by the team of Pr. Konrad from the University of Zurich, Switzerland, Intermittent fasting improves metabolic flexibility in short-term high-fat diet-fed mice.
Intermittent fasting refers to not eating for a set period each day. This diest proved to reduce metabolic inflexibility and improve insulin sensitivity.
The critical point is not to cut all the calories overall but to eat during a defined and short period.
Exposure to cold and hibernation
Even though the exposure to cold in hibernators improved metabolic flexibility and thus the increased use of lipids, this method is hardly usable in humans even though therapies with liquid nitrogen claimed that cryotherapy was beneficial to lose weight.
To wrap up
Metabolic flexibility is at the core of how the body learns to survive in times of starvation. Mitochondria are the primary regulator that will help to choose the right metabolic pathways.
Our current lifestyle is associated with the abundance of food leading to excess adipose tissue and a decrease in insulin sensitivity.
Metabolic inflexibility consequences can be severe for the health and carry an increased risk for type II diabetes, metabolic and cardiovascular disease, and even cancer.
Improving metabolic flexibility is not easy and involves exercising and limiting caloric intake. New devices such as the Lumen metabolic tracker offers the possibility to quickly check on the evolution of how your mitochondria regulate the fuel consumption choice.
