We've all heard that if someone is skinny despite eating enormous amounts of food, they have a high metabolism. On the same token, we've all heard that if someone is overweight despite eating small amounts of food, they have a low metabolism. On the surface this seems like it makes sense. However, upon further inspection we find that this just isn't true. You see, the one thing that people seem to misunderstand is the word metabolism itself.

So what is metabolism? To answer that, we need to delve into the incredible world of biochemistry!

Okay, First Question: Do I Get to Blow Things Up??

Oh how I wish...

If you're anything like me, your relationship with chemistry is complex, consisting of hate, fascination, frustration, and respect. How one science can induce immense rage and endless curiosity at the same time is beyond me. Don't get me wrong, I really do love chemistry. Once you have some perspective to its applications, the entire science becomes extremely interesting. It's just been in my experience that most people don't appreciate chemistry from their first initial exposure. So if that's you, hopefully this will be a whole lot more fun.

However, we're only going to speak to the need to know aspects, which coincidentally also happen to be the most interesting aspects. Each one of the topics we discuss today will have a rabbit hole for you to jump down if you so wish. At a later date, I fully plan on jumping head first into the chemistry rabbit hole, but for now, we're just going to stick to the basics.

Let's get to it!

Metabolism... It's Probably Not What You Think It Is

Most people seem to think that metabolism means the breakdown of food. I don't know how many conversations I've had over the years that demonstrate this, but let's just say it's a lot. However, this is a gross misinterpretation of the word. In fact, it completely omits half of what metabolism is. So if that's not what metabolism is, what is it?

Metabolism is best thought as the overall sum of chemical reactions that occurs in the body. That includes the buildup of molecules, as well as the breakdown of molecules. We even have special words that fall underneath the umbrella of metabolism: anabolism and catabolism.

Anabolism is the name for building up molecules, while catabolism is the name for breaking down molecules.

Let's say that in the name of science, we're going to eat lunch. You unpack your Power Ranger lunchbox, finding a Capri Sun, Reeses Peanut Butter Cup, and a nice turkey sandwich.

Mmmmmm...... Energy....

Upon taking that first delicious bite, your body begins to take the necessary steps to get as much nutrition as possible from the sandwich. In physics speak, nutrition roughly equates to energy, and energy allows the body to do work. For our purposes, you can think of work as simply doing stuff, like walking up the stairs, scratching your head, or eating a tasty sandwich.

First off, an enzyme in your saliva begins to catabolize the amylose sugar molecule in the bread, providing you with a nice sweet taste as you chew. This process includes what is called hydrolysis, which is the breaking of a chemical bond, and the adding of a water molecule to the broken pieces. Essentially, it's dissolving in water.

The turkey sandwich still has a way to go in order for its energy to be extracted. Saliva isn't powerful enough to catabolize the entirety of the bite, so instead it lubricates the chewed up food so it can more easily slide its way down your esophagus towards your stomach.

Once it finds it's way to your stomach, it's met with a good ol' fashioned acid bath.

Hydrochloric acid is what's considered a strong acid, and it's sitting inside of you right now. In fact, if you've ever experienced heart burn, you've definitely felt the wrath of this acid. If you're at all familiar with the pH scale, hydrochloric acid is sitting on the far end of the acidic spectrum.

Credit: http://thebaseisunderasalt.weebly.com/ph-scale.html

Your stomach's purpose is to further break down the food and drink that you put into it, so that the small intestine can gather the nutrition the body requires. The thing is, digested material needs to be extremely small in order to fit through the tight fitting epithelial cells that line your digestive tract.

The food material is bathed in the powerful acid, being ripped apart by the chemistry until it's a nice liquidy consistency that we now call chyme. Chymes purpose in life is to break everything it can into the smallest possible pieces. Remember, from a metabolic point of view we are still in the process of catabolzing the food material.

The chyme is now emptied into the small intestine, where it is met with bile and pancreatic enzymes designed to neutralize the acidity of the hydrochloric acid. After all, torching and scarring the intestines isn't really the most efficient way to do things.

The small intestines purpose is to extract the nutrients from the chyme. It accomplishes this through tiny little appendages called villi, that are loaded with blood vessels called capillaries. We'll discuss each of those structures in greater detail at a later date, but for now simply think of them as the necessary extractors of nutrients.

Credit: http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/common_systems/digestionrev5.shtml

As the nutrients are pulled into the capillaries of the intestinal lining, the remainder of the material is considered indigestible, and will continue to make its way through the digestive tract until the majority of it is expelled out the rectum. We'll revisit that process at a later date, because let's be honest, who doesn't love talking about poop?

They're Like Legos... Except They Don't Hurt Your Foot

There isn't much point in breaking down the food material into smaller pieces unless they're eventually going to be built back up into something useful. It's this process of rebuilding that we call anabolism, and it's the second half to metabolism.

Credit: https://online.science.psu.edu/biol011_active002/node/4163

Food material is more or less built of just a few types of molecules. Proteins, lipids, and carbohydrates. These are called macromolecules, and they are so vitally important to your existence, each one will get their own blog post to fully explain their awesomeness. But for now, it's probably easiest to think of them as building blocks.

Recall that originally water was added to the food material during chewing, and through the process of hydrolysis some of the material was broken down. In order to fully build things back up into something we can use, that same water must be removed through a process called dehydration synthesis. It's literally the opposite of hydrolysis.

Once the water is removed, anabolism can occur. Those very basic building blocks are reassembled into new macromolecules that the body can shuttle to the appropriate area to be used accordingly. This entire process can be likened to stripping an old vehicle down for the parts. While some parts of the vehicle will inevitably become waste, other parts can utilized for another function. Even the frame can used if so desired.

I want to make an important clarification here: what I have just described is one example of your metabolism at work. There are countless other examples that can be made, most of which are at a much smaller scale.

For instance, your immune cells will catabolize invaders, breaking them down into basic building blocks that can then be anabolized into something the body can use. It can be beneficial to think of your body as a giant recycling center.

If your body can utilize it somehow, it will.

Things like fiber are unable to be catabolized from your bodily fluids, so they must be excreted. However, as we'll see in our upcoming post on carbohydrates, even fiber can be made useful to our body by acting like a broom for you colon.

So what is metabolism? Metabolism is the word for the overall sum of every chemical reaction that occurs in your body. It's both the breakdown and buildup of bio material. Do you see now why it makes no sense to say that you have a low or high functioning metabolism? At this point, my only response is basically, "me too..."

Tip of the Nutritional Iceberg

We have only scratched the surface when it comes to the biochemistry of the body. When it comes to nutrition, there is always more that can, and should be said. In fact, soon I will be starting a Let's Learn Nutrition!!! blog series, so that we can understand more fully how our body utilizes and functions off of what we eat.

But before we can do that, we need to learn more about the building materials themselves. In our next post, we'll learn all about our first macromolecule, the protein. Spoiler alert!!! It isn't just for body builders!!

See ya next time!!

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In case you missed the earlier posts in the series:
Let's Learn Anatomy!!! #1
Let's Learn Anatomy!!! #2

Here are a few other posts that might interest you:
Why is Your Butt So Big??
Why Are Human Babies So Incredibly Weak??
Evolution, Society, and Cryptocurrency... How Does It All Relate???