Metabolism & Nutrition, Part 1: Crash Course Anatomy & Physiology #36

Summary

This video explores the intricate processes of human metabolism, detailing how our bodies convert food into energy and raw materials for growth and repair. It explains how anabolic reactions build up structures using energy, while catabolic reactions break them down to release energy. The video highlights essential nutrients like water, vitamins, minerals, carbohydrates, fats, and proteins, and their roles in sustaining life. By illustrating the continuous cycle of breaking down and rebuilding molecules, it provides a fascinating look into how metabolism sustains our bodies at a cellular level.

Takeaways

• 💧 64% of the body is water, and it plays a critical role in maintaining our form and function.
• 💪 After water, 16% of the body is made up of protein, which is crucial for muscles, enzymes, and various cellular functions.
• 🍔 Another 16% of the body is fat, which provides energy storage, insulation, and is essential for overall health.
• ⚖️ The body's metabolism consists of two types of reactions: anabolic reactions, which build up molecules, and catabolic reactions, which break them down.
• 🔥 Metabolism isn’t just about how fast you burn energy; it’s a complex system of all the biochemical reactions in the body.
• 🍞 Carbohydrates are primarily broken down into glucose, which is essential for energy, particularly for the brain and red blood cells.
• 🥩 Fats and proteins are not just energy sources; they play vital roles in cell structure, hormone production, and various biological functions.
• 🧠 Omega 3 and 6 fatty acids are essential because the body cannot produce them, and they play critical roles in brain function and inflammation.
• 🍗 Proteins from food are broken down into amino acids, which are then reassembled to form the proteins that make up your body.
• 🔄 The body is constantly rebuilding itself by breaking down nutrients and synthesizing new components, making metabolism a never-ending process.

Q & A

What percentage of the human body is made up of water?

The human body is approximately 64% water, which plays a crucial role in various bodily functions.

What are the primary components of the human body after water?

After water, the human body is composed of 16% protein, 16% fat, 4% minerals, and 1% carbohydrates.

What is the role of protein in the body besides building muscle?

Protein is not just for muscles. It is involved in various functions, including sodium-potassium pumps in neurons, hemoglobin in blood, and enzymes that drive chemical reactions in the body's cells.

Why does the body constantly require new chemicals and nutrients?

The body requires new chemicals and nutrients because its components, like enzymes and cell membranes, wear out, break down, or become oxidized over time. Thus, these must be replenished to maintain proper function.

What is metabolism, and how does it relate to the body’s processes?

Metabolism refers to all the biochemical reactions happening in the body. It includes anabolism (building up molecules) and catabolism (breaking down molecules), both of which are essential for energy production and repair.

How do anabolic and catabolic reactions differ?

Anabolic reactions construct larger molecules from smaller ones and require energy, while catabolic reactions break down larger molecules into smaller ones and release energy.

What are the six major groups of nutrients essential for the body?

The six major nutrients are water, vitamins, minerals, carbohydrates, lipids (fats), and proteins.

Why are carbohydrates important for the body’s energy needs?

Carbohydrates, specifically glucose, are the primary source of energy for cells, especially neurons and red blood cells, which rely almost exclusively on glucose for energy.

What is the importance of lipids (fats) in the body?

Lipids store energy, cushion organs, form cell membranes, and assist in storing fat-soluble vitamins. They also play a role in myelin formation for neurons and hormone production.

Why do proteins play such a crucial role in the body?

Proteins form muscle and connective tissue, ion channels, pumps in neurons, and enzymes that drive every chemical reaction in the body, making them essential for overall function.

Outlines

00:00

💧 The Composition of the Human Body

The speaker explains that their body, weighing 80 kilograms, is composed mainly of water (64%), proteins (16%), fats (16%), minerals (4%), and carbohydrates (1%). They describe how the body continually acquires, uses, and disposes of these elements, constantly rebuilding itself. Over a lifetime, a human will synthesize hundreds of kilograms of protein. The process of metabolism — involving both breakdown and reconstruction of molecules — keeps the body functioning. The discussion sets the stage for understanding how the digestive, endocrine, circulatory, and respiratory systems are interconnected, and emphasizes that metabolism is a continuous cycle of breaking down nutrients and rebuilding the body.

05:02

⚡ Metabolism: The Energy Process

This paragraph explores how the body converts food into energy through metabolism, focusing on glucose as the primary fuel for creating ATP, the energy currency of cells. While some cells can derive energy from fats, crucial cells like neurons and red blood cells rely solely on glucose. Excess energy from carbohydrates is stored as glycogen or fat for future use. Lipids, although often misunderstood, are essential for storing energy, protecting organs, and supporting brain function. The liver plays a key role in converting different types of fatty acids, including omega-3 and omega-6, which are vital for brain and body health.

10:04

🍗 Proteins: The Building Blocks of Life

The focus shifts to proteins, which are crucial for nearly every bodily function. Proteins form muscles, connective tissues, enzymes, and ion channels that drive essential processes. Everything we eat, once alive, contains proteins, and our bodies break these down into amino acids before reassembling them into human-specific proteins using DNA. While the body can convert some amino acids, nine essential amino acids must come from food. The paragraph highlights the importance of combining foods to ensure a complete supply of amino acids and reaffirms the role of proteins as the foundation of bodily structure and function.

📊 Nutrient Breakdown and Metabolic Overview

This final paragraph recaps the six vital nutrients — water, vitamins, minerals, carbohydrates, fats, and proteins — and describes how anabolic and catabolic reactions work together in metabolism. Anabolic reactions use energy to build the structures in the body, while catabolic reactions release energy by breaking down substances. Together, these processes drive metabolism, the complex but necessary system that keeps the body functioning. The paragraph concludes with acknowledgments to the creators and contributors of the video, emphasizing the collaborative effort in bringing educational content to viewers.

Keywords

💡Metabolism

Metabolism refers to the total of all biochemical reactions occurring in the body, enabling it to acquire, process, and utilize nutrients for energy and maintenance. In the video, metabolism is presented as a continuous process that includes breaking down food for energy (catabolism) and building new cellular materials (anabolism). It's described as a never-ending cycle, essential for maintaining life.

💡Anabolism

Anabolism is a type of chemical reaction that constructs complex molecules from simpler ones and consumes energy in the process. This concept is central to the video as it highlights how our bodies use small building blocks like amino acids to form proteins and other polymers needed for cell functions. For example, when proteins are synthesized from amino acids, it's an anabolic process.

💡Catabolism

Catabolism involves the breakdown of complex molecules into smaller units, releasing energy. This process is crucial for generating the fuel that the body uses to sustain itself. The video illustrates how carbohydrates, fats, and proteins are catabolized to release energy, which is then used to power various cellular processes.

💡Nutrients

Nutrients are substances that organisms need to survive, grow, and reproduce. The video identifies six major groups of nutrients—water, vitamins, minerals, carbohydrates, fats, and proteins—each serving a unique purpose in the body, from providing energy to supporting cellular functions. Nutrients are the foundation of both anabolic and catabolic processes.

💡Proteins

Proteins are large, complex molecules that perform a wide variety of functions in the body, such as forming muscle tissue, enzymes, and ion channels. The video explains that proteins are made of amino acids and that the body constantly synthesizes them through anabolism. Protein accounts for about 16% of the body and is essential for its structure and function.

💡Carbohydrates

Carbohydrates are one of the body's primary sources of energy, particularly glucose, which cells, especially neurons, use to produce ATP. The video emphasizes that carbohydrates come from plant-based foods like grains and fruits, and that they play a vital role in fueling anabolic reactions and storing energy in forms like glycogen.

💡Fats

Fats, or lipids, serve as energy storage, insulation, and building blocks for cell membranes. The video highlights the importance of fats, not only for energy but also for storing vitamins and forming essential molecules like hormones. Fats also contribute to brain health and provide energy in the form of triglycerides.

💡Vitamins

Vitamins are organic compounds that help regulate various biochemical processes. The video explains that, although vitamins don’t provide energy, they are essential for metabolic functions, such as vitamin C improving iron absorption and B vitamins aiding in ATP production. They are classified into fat-soluble and water-soluble categories.

💡Minerals

Minerals are inorganic elements that contribute to bodily functions such as bone health, blood oxygenation, and nerve signaling. The video identifies minerals like calcium, phosphorus, and iron as key contributors to processes like bone formation and oxygen transport, emphasizing their role as vital nutrients even though they don't directly supply energy.

💡ATP (Adenosine Triphosphate)

ATP is the primary energy carrier in cells, driving many anabolic reactions. The video describes how cells use ATP to perform various tasks, from muscle contraction to active transport in neurons. Although ATP cannot be stored, glucose is metabolized to create ATP when energy is required by the body.

Highlights

64% of the human body is made up of water, with protein making up 16%, and fat also 16%.

4% of the human body is composed of minerals, including calcium, phosphorus, and iron.

1% of the body consists of carbohydrates, mostly used for energy or stored as glycogen.

Over a lifetime, the body synthesizes between 225 and 450 kilograms of protein, enough to rebuild the body multiple times.

Metabolism consists of two major processes: catabolism (breaking down molecules for energy) and anabolism (building up molecules using energy).

Water, vitamins, minerals, carbohydrates, fats, and proteins are the six essential nutrient groups for the body.

Monosaccharides, like glucose, are the primary fuel for the body, especially for neurons and red blood cells.

Carbohydrates not needed for immediate energy are stored as glycogen or converted to fats.

Fats provide energy storage, insulation, cushion organs, and play a crucial role in cellular membranes and hormones like testosterone and estrogen.

Essential fatty acids, like omega-3 and omega-6, cannot be synthesized by the body and must be ingested.

Proteins are essential for muscle formation, enzymes, ion channels, and nearly every chemical process in the body.

The body uses 20 amino acids to build proteins, with nine of them being essential and needing to come from the diet.

Catabolic reactions break down food into molecular components that can be reassembled through anabolic processes.

The body's cells constantly undergo both breakdown and rebuilding, similar to the myth of Sisyphus endlessly pushing a boulder uphill.

Vitamins and minerals help the body absorb other nutrients and perform crucial functions like improving iron absorption, aiding blood clotting, and supporting ATP production.

Transcripts

I weigh about 80 kilograms.

Most of that, let’s say 64 percent, is water -- though you can’t tell by looking.

I mean, as organisms go, I like to think that I look fairly solid.

After water, the next largest proportion of me is protein, about 16% -- not just in my

muscles, but also in things like the tiny sodium-potassium pumps in my neurons, and

the hemoglobin in my blood, and the enzymes driving the chemical reactions in every one

of my 37 trillion cells.

Then another 16% of me is fat, which I’m totally OK with;

Four percent of me is minerals, like the calcium and phosphorus in my bones, and the iron in my blood;

and 1 percent is carbohydrates, most of which is either being consumed as I talk to you,

or is sitting around as glycogen waiting to be used.

But here’s the thing: It’s not like I just ate 80 kilograms of food and then all this happened.

Instead, my body, like yours, is constantly acquiring stuff, extracting some of it to

keep, burning some of it for energy, and getting rid of the rest.

But even the stuff that my body does hold onto doesn’t last forever. Some of the chemicals

that I absorb in my food eventually become a part of me. But enzymes wear out, and membranes

break down, and DNA gets oxidized. So, they get discarded.

And then I need more of those chemicals to reconstruct the material that I’ve lost.

As a result, over the course of my lifetime, my cells will synthesize somewhere between

225 and 450 kilograms of protein …

That’s like 3, or 4, or 5 separate me’s -- just made of protein.

And all of the protein and fat and carbohydrates nucleic acids that

make up me, of course, come from food.

Every organism has to keep taking in and breaking down food, to keep resupplying itself with

the raw materials it needs to survive.

And all that activity requires energy, which we also gain from food.

So, how do our bodies actually convert what we eat into energy and raw materials?

The answer is a neverending series of reactions that are dedicated to doing two vital, and

totally contradictory, things:

One set of chemical reactions destroys the reactants that you give them, reducing big,

complex substances into molecular rubble.

And the other set reassembles that rubble into new and bigger products that are put

together again to make you.

So our bodies are constantly reinventing themselves -- in a perpetual state of loss, but also always rebuilding.

And even though all of this is happening at the cellular level, its consequences could hardly be larger.

These two sets of reactions are where everything that we’ve learned so far -- about the digestive,

endocrine, circulatory, and respiratory systems -- really starts to come together.

Together, these processes make up your metabolism.

Now the sciencey word metabolism has come to have a meaning in popular speech,

but metabolism isn’t just one thing.

People talk about metabolism as meaning, like, how fast your body burns the fuel in your

food, or how high your personal energy level is.

And that’s fine for use by personal trainers and fitness magazines.

But physiologically, metabolism really describes every single biochemical reaction that goes on in your body.

And maybe more importantly, it reconciles two conflicting chemical processes that are

always, simultaneously underway inside of you.

One of those chemical forces is anabolism.

Anabolic reactions construct things and consume energy.

These are the processes that take the small monomer building blocks in your food -- like

monosaccharides and fatty and amino acids -- and build them into bigger, more complex

polymers like carbs, and fats, and proteins that are used in your cells.

Then, when you need new building blocks, or you need to release some energy, those polymers

in your body, or new ones in your food, get broken up -- by catabolic reactions.

The processes of catabolism break down bigger molecules, and in breaking their bonds, release

the energy you need to stay warm, and move around, and provide your cells with fuel … to

build the polymers back up again.

To be honest, your metabolism is a lot like Sisyphus. It works really hard. But it is never finished.

And the boulder that your inner Sisyphus is always pushing uphill and watching fall back

down? That’s nutrients -- the molecules that your body is forever breaking up, and

then rebuilding, only to have them break apart again.

And these nutrients -- the materials your body needs to build, maintain and repair itself

-- come in six major groups.

By volume, the majority of what we consume -- and what makes up our bodies -- is water,

so that’s maybe the most vital nutrient.

Then there are vitamins, compounds that come in either fat-soluble or water soluble forms.

They aren’t used as building blocks or for energy, but they’re essential in helping

the body make use of other nutrients that do do those things.

Vitamin C, for example, helps improve iron absorption, while vitamin K is crucial to

blood clotting, and some B vitamins are important in the production of ATP from glucose.

Minerals, like vitamins, they don’t provide fuel, but they have all sorts of other functions.

Calcium, magnesium, and phosphorus harden bones and teeth, while iron is, of course,

crucial in hemoglobin. Plus, potassium, sodium, and chlorine help maintain your body’s pH

balance and are used in action potentials.

So water, vitamins, and minerals are all … necessary.

But the three major nutrients that everyone always talks about -- the ones you find on

food labels, from oatmeal to Pop-Tarts -- are carbohydrates, lipids, and proteins.

Most of the carbohydrates you’ve ever eaten

-- with the exception of lactose in milk -- originally came from plants.

Mono- and disaccharides come from fruits, honey, sugar beets and sugar cane, while polysaccharide

starches come from veggies and grains.

The main thing you need to know is that the monosaccharide glucose is the be-all-end-all

molecular fuel that your cells need to make ATP.

ATP being the molecule that your cells use to drive anabolic reactions, when they need

to make new polymers or get anything else done -- whether that’s operating a sodium-potassium

pump, or detaching the head of a myosin filament to contract a muscle.

But ATP is too unstable to store, so cells often store energy in the form of glucose,

which they can then catabolize and convert to ATP when they need it.

Now, some of your cells can get their energy from fats. But many of the most important

ones, like your neurons and red blood cells, feed exclusively on glucose. So most of the

carbs that your intestines absorb are converted to glucose for that reason.

But, if it’s not needed right away, that energy can also get stored as glycogen in

your liver and muscles, or converted to glycerol and fatty acids to make triglyceride fats.

And even though there seems to be a marketing war going on against dietary fats,

we most definitely need them.

The fats in your adipose tissue store energy, of course, but they also store fat-soluble

vitamins, and cushion your organs.

Lipids also form the myelin that insulates the neurons in your brain and throughout your

body, as well as the oil in your skin, and they provide the vital calorie content found in breast milk.

But there are other important lipids, like cholesterol, which is the precursor to things

like testosterone and estrogen...

...and, of course, phospholipids, which form the cell membrane in every single one of the

three-dozen-or-so-trillion cells you have.

Now, if you’re into eating meat, a lot of the fat that you ingest might come from that.

But guess what: Plants have fat too.

Plants use lipids for energy storage just like we do, except they do it in fruits, and

nuts, and seeds. Which, when you think of it, are kind of like plant breast milk -- it’s

food for their growing babies.

Either way, though, when you eat lipids, your body breaks down triglycerides into glycerol

and fatty acids.

Those molecules can then be processed and used in the making of ATP. Or they might be

converted into other kinds of fatty acids, which your cells can then re-assemble into

your very own triglycerides or phospholipids.

And your liver happens to be great at converting one fatty acid into another, but there are

some it just can’t synthesize.

For example, omega 6 and 3 fatty acids are called essential fatty acids, because your

body can’t make them, so they have to be ingested.

They get turned into all kinds of useful molecules, like the ones used for synapse formation in

the brain, and for signalling inflammation during the healing process.

But -- if carbohydrates provide energy, and fats insulate and store energy, then just

about everything else is done with proteins.

They form the bulk of your muscle and connective tissue, but they’re also what the ion channels

and pumps are made of in your neurons and muscle cells, and they make up your enzymes,

which are responsible for pretty much every chemical reaction in your body.

In other words, your body runs on protein, and pretty much is protein.

Nutritionally speaking, meats, dairy products, eggs, legumes, nuts, cereals are particularly

high in protein. But because everything we eat was once alive, and every cell of every

living thing contains protein, as long as you’re eating whole foods, you’re at least

partially re-stocking your protein supplies.

Now it might seem like you’d have eat muscle to make muscle, or eat enzymes to make enzymes,

but that’s not how it works.

Since all of your proteins are made up of just 20 amino acids, the differences between

the thousands of unique proteins are simply in the sequence of those amino acids.

And, of course, you have a specialized molecule that knows just which amino acids to put together

in what order to make a certain protein.

It’s called DNA.

When you consume some hamburger, for example, the protein actin in the meat gets catabolized

into its component amino acids, which gets mixed up with all the amino acids from the

other proteins in the meat -- like the collagen and elastin and titin and myosin -- as well

as all the protein from the bun and the tomato and the mayonnaise.

Those amino acids then get reassembled using anabolic reactions into your very own, but

somewhat different, proteins, as defined by your DNA.

Each cell is like a picky little Gordon Ramsay and it has to have every amino acid needed

-- every ingredient present -- before it will even think about starting to make a protein.

And just like with your lipids, your cells can improvise, and convert some amino acids

to others if they’re missing an ingredient.

However, there are nine essential amino acids that you cannot make from others, and have to eat.

Now lots of foods don’t provide every essential amino acid, but when you combine foods, like

beans and rice, or pasta and cheese, you do get all of the essential amino acids. Which

is important because, remember: after water, you are mostly made of protein. On the order of 16%

But what about the one percent of you? The carbohydrates?

How that tiniest fraction of you ends up creating all of the energy, is what we’ll discover next time.

But for now, you’ve learned all about the vital nutrients -- including water, vitamins,

minerals, carbs, fats, and proteins -- as well as how anabolic reactions build structures

and require energy, while catabolic reactions tear things apart and release energy. And

together, these competing forces form the wonderfully conflicted process known as metabolism.

Thank you to our Headmaster of Learning, Linnea Boyev, and thanks to all of our Patreon patrons

whose monthly contributions help make Crash Course possible, not only for themselves,

but for everyone, everywhere. If you like Crash Course and want to help us keep making

videos like this, you can go to patreon.com/crashcourse

This episode was filmed in the Doctor Cheryl C. Kinney Crash Course Studio, it was written

by Kathleen Yale, edited by Blake de Pastino, and our consultant is Dr. Brandon Jackson.

It was directed by Nicholas Jenkins, edited by Nicole Sweeney; our sound designer is Michael

Aranda, and the Graphics team is Thought Cafe.