Blood glucose monitoring: metabolic foundations and contextualization
Introduction
As we will explore throughout this post, blood glucose, or the concentration of glucose in the blood, is a physiologically significant variable for both health and athletic performance. The amount of glucose in the blood is a precise response of the human body to varying degrees of metabolic need. Much like a Swiss clock, the human body operates its regulatory mechanisms to maintain adjusted glucose levels. Thanks to advancements in science and technology, we have come to understand its importance, how it is regulated, its metabolism, and, most importantly, what ranges are optimal for different physiological situations and their relation to health and disease.
In recent years, and thanks to these advancements, glucose monitoring has become “democratized” through interstitial fluid measurement sensors, allowing us to track this fascinating physiological variable ourselves. Here’s the first insight: current measurements (using the sensors we all know) are not taken directly from the blood but rather measure glucose oxidation in interstitial fluid. Why is this possible? Because, due to various gradients, glucose, minerals, and fluids, among other components, tend to equalize between the blood and interstitial space (the area surrounding cells and organs, in this case, close to the skin), although with a slight delay (5-10 minutes). This bodily mechanism allows us to correlate and estimate blood glucose levels with a high degree of validity through such measurements.
Knowing each person’s blood glucose levels is incredibly valuable as it provides insights into one of the most relevant variables in health and performance. However, it also allows us to analyze information that is very sensitive and variable under different circumstances, and, like everything in human biology, its evaluation must be approached with a thorough understanding of the involved mechanisms. Blood glucose is a powerful tool if we know how to use it, and for that, a rigorous understanding of its dynamics is necessary. To assist you in this learning process, based on the latest scientific evidence and our expertise and research as professionals in the field, we welcome you to this educational blog. Let’s start learning more about it!
Metabolic regulation of blood glucose
As we’ve discussed, maintaining blood glucose levels within homeostatic values (which vary depending on the situation, as we’ll see in future posts) is a primary objective for the human body. This highlights the critical role of glucose as an energy substrate for the various cells that make up the organism. Therefore, the body employs multiple mechanisms to keep blood glucose levels within a biologically favorable range. What are these mechanisms?
In brief, we can say that the liver acts as the thermostat for blood glucose in the body, as it is the primary organ responsible for regulating it. The liver metabolizes various substrates, including carbohydrates, fatty acids, and amino acids (or proteins), each with different goals. One of its most crucial functions is to ensure adequate glucose availability. For example, when carbohydrate availability is high (due to a high intake from the diet), the liver releases the necessary glucose (as determined by peripheral tissues) into the blood to be transported where it’s most needed. During exercise, for instance, skeletal muscle is the most significant consumer of glucose. Conversely, when carbohydrate availability is low, the liver catabolizes certain amino acids and proteins to produce the necessary glucose and release it into the blood for the same purpose. In extreme fasting or chronic low carbohydrate availability, the liver also metabolizes and “distributes” various fatty acids, such as ketone bodies, and cells adapt to use them due to the scarcity of glucose.
Now, who provides the signals to the liver to open or close the gates of entry and/or exit?
Considering that metabolism is a precise and intricately coordinated machine (which makes it fascinating), we can imagine a well-coordinated regulation system controlling liver activity. To make the understanding of these mechanisms more accessible, we will highlight five main factors that regulate glucose availability. In reality, these five factors are closely interconnected and dependent on each other.
Hormonal activity
In very brief terms, the two most important hormones in glucose regulation are glucagon and insulin. Both are secreted by the pancreas and play distinct roles. While glucagon stimulates the release of glucose from the liver, insulin promotes the uptake of glucose into tissues (primarily peripheral tissues). A tight balance between these two hormones, which respond to various physiological conditions, maintains blood glucose levels within biologically appropriate ranges.
Nervous system
The nervous system plays a key role in regulating blood glucose levels, particularly in the release of glucose from the liver. Although it is distinct, this system is closely related to hormonal responses. During exercise or stressful situations, the sympathetic nervous system is activated, sending signals for the secretion of various hormones and neurotransmitters that are crucial for glucose regulation. Among these are adrenaline, noradrenaline, and cortisol. Conversely, when the parasympathetic nervous system is activated, the effect is antagonistic. Additionally, various neurotransmitters or peptides, such as those regulating appetite, can independently influence blood glucose levels, separate from hormonal effects.
Cardiovascular system
Both centrally and peripherally, the cardiovascular system, through the nervous system, also regulates glucose availability. Especially during exercise, adjustments in blood flow are likely the primary stimulus for glucose entry into peripheral tissues such as skeletal muscle.
Internal availability of energy substrates
One of the factors that most affects glucose regulation is the availability of substrates, primarily in the liver. Depending on whether there is more glucose and/or glycogen in the liver, the regulation will vary. This always depends, too, on the external demand for substrates.
External demand or needs
Finally, the body’s need or demand plays a crucial role in balancing blood glucose levels. Often mediated by the nervous system and various neurotransmitters, the body can interpret external demands (such as those from muscles during exercise or from a tumor cell during cancer) and adjust its control mechanisms accordingly, “sending” more glucose to these specific destinations.
Why is it important to understand blood glucose levels?
Blood glucose concentration is therefore a highly sensitive physiological value that can predict various situations or capabilities of individuals. However, as you might have inferred from the previous point, it is subject to multiple variables that can occur in very different situations, and without the proper context and understanding, this can lead to misinterpretation. For example, during moderate-to-high intensity exercise, a physiological mechanism in the human body is to raise blood glucose levels (to supply glucose to the muscles), sometimes reaching values even higher than 160-180 mg/dL. These levels, in a different situation, could pose a health risk, especially if sustained over time. Similarly, with the same food intake, blood glucose levels can vary because physiological situations can influence the body’s priorities. For example, if a person is experiencing high stress or anxiety (due to reasons such as heavy workload, concerns, or intense training), their blood glucose response may increase as a result, leading to higher values.
In the same way, and as we will discuss in the next section, this can lead to false interpretations, such as with the intake of different foods. For instance, when consuming low-carbohydrate foods or following a low-carb diet, we generally observe a downward trend in blood glucose levels, maintaining values that are considered healthy (80-110 mg/dL). This might lead us to interpret and assume that our metabolic health is better with such intakes. However, this is not necessarily the case. An acute increase in blood glucose after food intake is a natural mechanism that does not necessarily indicate poor metabolic health. The ability to regulate or introduce glucose into peripheral tissues is the variable that could be related to metabolic health and differentiate a healthy individual from one with metabolic disease. This interpretation may be a fine line that is difficult to distinguish but can represent a significant difference.
Therefore, it is not only important to understand what blood glucose levels mean and why they may increase or decrease but also to comprehend them within the exact context in which they are analyzed. This includes considering dietary intake, physical movement or exercise, and the individual’s specific situation.
What it represents and what it doesn’t represent
To avoid misunderstandings, it’s important to know exactly what blood glucose levels represent. At Glucovibes, we understand that measuring blood glucose has its possibilities and limitations. It’s all about knowing precisely what physiological variable you’re dealing with, its value, and its significance. Nothing more, nothing less. It’s neither a cure-all nor something meaningless. Recognizing its true importance will make it a valuable tool for understanding, predicting, and improving your health and athletic performance. However, assigning attributes it doesn’t have can lead to serious misinterpretations. So, let’s clarify what blood glucose levels represent and what they do not:
What it represents: Primarily, and to be somewhat precise, it represents the difference between its “output” from the liver and its “input” into peripheral tissues. More specifically, it represents a concentration, so it can vary if the total blood volume changes. It also indicates the amount of glucose being “sent” at that moment to peripheral tissues and, therefore, could be a measure of the absorption capacity of those tissues. On a more global level, it represents the adequacy (good or bad) of the body’s response to a situation, as it is an indirect measure of a subject’s readiness for a task (why, otherwise, does it rise during exercise, even in a fasted state with no food intake?). Finally, following this line, glucose levels could also be a predictive value, especially in chronic trends, indicating a lack of health or the presence of metabolic disease with multiple causes, suggesting that glucose metabolism and its regulatory mechanisms are failing. And that’s it. As such, it only represents this. However, with a good understanding of metabolism, it can mean much more.
What it does not represent: It does not represent, nor is it an indirect measure of, the amount of substrate (fuel) in the body, let alone the amount of glycogen, primarily at the muscular level. In conditions of low glycogen availability, even in the liver, the body uses other substrates to produce glucose and maintain blood glucose levels, so it does not have a direct relationship with this energy status. It also does not indirectly represent, as is often misunderstood, the metabolism and oxidation of fatty acids. Low blood glucose levels do not mean increased fatty acid metabolism and oxidation. For example, elite endurance athletes achieve their maximum rate of fatty acid oxidation at a moderate intensity that may correspond to a blood glucose level of 110-140 mg/dL. Finally, blood glucose levels do not represent a standard measure (and this is crucial to understand), as it is highly individual and can vary widely between individuals.
Conclusions
In summary, through this blog, we aimed to introduce you, rigorously and with current metabolic knowledge, to the fundamentals of understanding glucose dynamics. We have a powerful and intriguing physiological value at our disposal from which we can learn a lot to improve our health and performance. However, it could also be detrimental if we do not fully understand what it represents and the meaning of its values. At Glucovibes, our scientific team’s ultimate goal is precisely this: to educate and guide in the knowledge and interpretation of glucose levels so that everyone can benefit from its potential while managing its limitations.
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