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The Physiology of Insulin: The Poison of Plenty

example of physiology of insulin

 

Physiology of Insulin

The importance of diet has been an obsession of popular culture for many decades. However, amidst the passionate arguments that each health guru brings to the table, people fail to ask a simple question: how does the body burn fat? For example, all the weight watchers advocate low calorie diets. But does the body know how to count calories? By digging deeper into the biology, we must determine exactly what “language” the body speaks. This quest ultimately leads us to the ultimate solution: the physiology of insulin. 

Food and Hormones: The Language of Life

In order to understand why this is the case, we must first understand how the body sends messages to different organs. In essence, what “language” does the body speak in? Well, let’s think about it: what makes you tired, hungry, or happy? The correct answer is melatonin, ghrelin, and dopamine, respectively. In short: hormones are the messengers that carry commands that tell your body to do things. So, what hormone is associated with eating food? The answer is insulin. We need to understand the physiology of insulin.

Why Insulin?

The physiology of insulin explains why this hormone is essential for fat gain and loss. Essentially, whenever insulin is high in the blood, our body is constantly sending the message “store fat, there is enough food”. In order to accomplish this, our bodies have insulin receptors that tell fat cells to stop releasing fat due. This makes sense since high insulin usually means lots of energy is already present in the blood. Thus, when lots of food is coming in through the mouth, insulin stops the body from accessing fat, saving it for times of famine. This understanding of the physiology of insulin leads us to another question: if energy storage is essential for life, what stops us from eating to the point of death? This question brings us to the next character in our metabolic performance: leptin.

Feeling Stuffed…with Leptin

If you are reading this, odds are that you have experienced the feeling of being stuffed. I am talking about the feeling you get after eating a ton of food, where just thinking of eating something else makes you nauseous. This feeling may actually stay with you throughout the day and maybe even the next morning! If the body is an energy monger, this is a shocking development. An organism that needs constant energy to fuel the brain has natural eating limitations. How does the body send us this long term signal? 

The answer is leptin. This hormone is released when fat cells expand, telling the body that it is getting too fat. Why does the body limit how much we eat? The answer is because being too fat is not a survival advantage. After a certain point, excess fat will slow you down and affect the rest of your body in a negative way. Leptin thus counters insulin by lowering appetite and reducing the amount of sugar in the blood since the organism will not eat. This implies that less insulin will be needed when leptin is active.  Taken together, these two hormones create a negative feedback loop that maintains the body weight through appetite.

Now…back to the original question: what is the issue with calorie counting? 

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Biological Energy: Fueling Life in a Cold Universe

Harnessing Biological Energy

If someone asked me to describe the universe in one word, I would call it expansive. Expansion is the fundamental driving force behind everything that happens, from the simple life of an amoeba to the sun burning bright in the sky.

You can observe expansion in action when you breath out on a cold day, and see a white cloud spread out and fade. Simply put, everything that exists wants to spread out evenly unless something stops that from happening.

The Currency of Life

That something that resists this endless force is energy. Energy is the most valuable currency for any complex structure. In the case of planets holding themselves together, this is gravitational potential energy, in the case of life, it is ATP and thermal energy. Essentially, the use of energy is the only way to reorganize atoms in one’s surroundings. Energy must be spent whether a cell is trying to copy DNA or a person is walking from point A to point B.

The Most Important Forms of Energy

The two main sources of biological energy are chemical potential energy (ATP) and thermal energy (heat).

What is Chemical Energy?

Chemical potential energy is relatively easy to explain: in order to create and use organized molecules (proteins), energy must be added to the system. This type of energy is present in all organisms. Proteins will be discussed in a future post.

What is Thermal Energy?

Thermal energy is slightly less intuitive but equally important. Complex molecules need to be kept at a certain temperature to maintain their structure and function (future post) . To understand this, imagine a guitar string as a molecule; the harder you pluck the string, the stronger the vibration. At a certain point, the vibration will be too strong and the string will snap. The vibration can also be too weak resulting in no sound.

These analogies are almost exactly what happens. At high thermal energy, the bonds between atoms begins to break down (remember, biological energy is the driving force of change). Due to molecular collisions, the molecule loses its function. At low thermal energy, the bonds between atoms either become too rigid or find a less complex, more stable form which results in the loss of function.

Take us humans for example. Through evolution, we have developed many systems dedicated to keeping us together and resisting this endless force. Of course, our skeletal system holds us together but the laws of the universe works on things at every scale.

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